Get a Digiface USB and connect all Adats there

You are right.
May be sorting out that Motu switch will help ?

I believe on the 12mic you can change the number of channels & number of streams. There’s a section of the manual talking about output stream size.

Hmm, so you have the 12 mic setup as 2 streams of 8 channels each? You said above it was setup with a 12 channel stream.

The Motu manual seems to imply that you're better off using USB to connect to your Mac.  See pages 32 (the 2 interface diagram) to 35.  In particular there's a section that says this:

Multiple AVB Ethernet audio interfaces
When operating Monitor 8 as an AVB Ethernet
audio interface (“AVB Ethernet audio interface
setup” on page 32), multiple AVB audio interfaces
can be connected using a MOTU AVB Switch (or
any 3rd-party AVB switch), and the Mac can see all
of them through their AVB connection. For
example, you could connect an Avid S3 console to
the Mac, and then connect a MOTU Monitor 8 to
the S3’s extra network port (which is a built-in
switch). The Mac can see both Monitor 8 and S3
for audio I/O. However, OS X takes over each
device for exclusive use, so they can only stream
audio to and from the Mac, not each other. The
same is true for all AVB devices connected to the
Mac.

I'm not sure if this suggestion is welcome at this point. But since AVB is more complex in terms of setup and handling, I would switch to a proven MADI-based solution.

As your best preamp in the setup (RME 12Mic) supports MADI, this is easy to achieve. You are already about to purchase an RME recording interface (AVB), so you only need to change your plan a little bit to get one supporting MADI; see below.

As an option, you can purchase a 2nd 12Mic for a full MADI-based setup. Then every preamp can be remote controlled by TotalMix FX via "MIDI over MADI" over the fiber cable.

The optical fiber cables not only have the advantage of supporting up to 2km length between each of the MADI devices (which can be connected in a serial fashion), but the optical cable is also not so stiff and thick compared to an Ethernet CAT5/6 cable.

As a "compromise" (not having to buy a 2nd 12Mic immediately), you could also go for a mixed setup,
connecting your Focusrite Preamp through ADAT, same for the Motu Monitor 8.
As an alternative the Motu monitor 8 can be connected to the ADAT output of the 12Mic.
Then you route the monitoring flows through MADI and the routing to ADAT is being configured locally on the 12Mic.

if the other preamps support ADAT as well, e.g.:
UFX III----ADAT1------MOTU Monitor 8
          ----ADAT2------Focusrite Preamp
         -----MADI(o)----12Mic#1 (up to 5; one MADI bus supports 64 channels at single speed).

The advantages of using only 12Mics:

- everything over MADI
- higher max cable length (up to 2 km between MADI devices, also if multiple are chained in a serial fashion)
- Remote controllable via TotalMix (-> Auxdevice via "MIDI over MADI")
- Galvanic isolation, no issues with hum due to different ground potentials.

Another advantage of MADI over AVB is that you are independent of the AVB implementation in the OS, which can be a "moving target".

Clock synchronization is conveniently done via MADI (or Word Clock), and via "MIDI over MADI", the 12Mic can even be remotely controlled, either via TotalMix (Auxdevice) or alternatively via RME connector.

I would consolidate the setup to a MADI recording interface and then one or more 12Mic, which can be connected in series via MADI.

With MADI, when using multimode fiber (OM3, OM4 cables), the cable lengths can be 2 km between each individual device, and different MADI devices can be connected in series.

Example:

Location:            Control Room                   | Recording     Room1                         Room2                       Room3
                          clock master                                          slave                           slave                          slave
PC/Apple---USB---RME Recording Interface----[OM4]----->12Mic#1----[OM4]---->12Mic#2----[OM4]---->12Mic#3
                                        |                                                                                                                      |
                                        +-------------------------------<--------------[OM4]------------------------------------+

This allows for a good distribution of various mic preamps in different rooms or areas of a large location to keep the copper-based cabling as short as possible.

The cost of multimode cable is comparatively very low, as it is a standard cable used in networking. The cables are also slim and inconspicuous, making them easy to lay in existing cable ducts. In addition, MADI optical offers galvanic isolation between devices which is a big advantage, especially if you distribute the MADI components in different rooms/locations, where it is likely that you have different grounding potentials (don't know the exact english term, but you know what I mean).

On special order, the RME recording devices supporting MADI (MADIface USB, UFX III, HDSPe MADI FX, ..) can be ordered with "single mode", in which case the cable length between the devices can be up to 10 km.

The newer Preamps and AD/DA converter allow swapping of the SFP module (network transceiver) to support either single or multimode. By default, all RME recording interfaces are equipped with multi-mode, which should be more than sufficient for typical applications.

Advantages of MADI

- Longer cable lengths (OM3/4 multimode: 2 km, single mode 10 km between each of the MADI devices)
- Galvanic isolation (when using optical cables)
- Simple clock synchronization (master, slave)
- MIDI over MADI for remote controlling 12Mic, either via Auxdevice or RME connector

Remote controlling 12Mic

- Auxdevice, integrated into TotalMix FX, allows you to store the most important preamp settings in TotalMix FX Snapshots/Workspaces
- RME connector, a separate application, allows you to use either MIDI over MADI or LAN for remote controlling the devices. When using LAN, then also peak metering is possible, but then you need a LAN connection to the 12 mics.

RME recording interfaces with MADI support
- MADIface USB, USB2 based, simply MADI and MIDI over MADI, one MADI bus.
- UFX III, USB3 based, plenty of options, full implementation of FX, Room EQ/Crossfeed, MIDI over MADI, one MADI bus.
- MADIface XT II, USB3 based, little fewer options compared to UFX III, Room EQ/Crossfeed, MIDI over MADI, 3 MADI buses
- HDSPe MADI FX, PCIe based (**), full implementation of FX, RoomEQ/Crossfeed, MIDI over MADI, 3 MADI buses

(**) With an Apple, this would require an external Thunderbolt case additionally. I can't comment on whether this works reliably. Cases from Sonnet might be the most reliable solution; I wouldn't choose cheaper devices.
With the HDSPe MADI FX, you can buy an optional module that gives you a 3rd optical MADI bus.

If you were to choose between UFX III and MADIface XT II, my Excel comparison sheet may help you find out which feature set you prefer more. The UFX III has 4 preamps similar to the 12Mic with 75 dB gain and can also be used as an Instr (or line) input.
The MADIface XT has other preamps not supporting 75 dB, and they are not usable as Instr input. But it has 3 MADI buses, two optical, 1 coaxial.

If you plan to integrate an RME reference converter into your setup for the best monitoring features (ADI-2 Pro FS R BE or ADI-2/4 Pro SE), then the best solution would be the UFX III and HDSPe MADI FX. Both interfaces offer AES (UFX III also 2x ADAT) to integrate the reference converter into your setup.

MADI cabling, SFPs (Transceiver)

For multimode you can use OM3 or OM4.
Best is to stick to one cable standard, this is really needed when using in house cabling, a mix of fix stationary cabling, patch fields and patch cables. If you would mix the fiber cable types on an optical connection, then you get dampening and this can cause errors. As a rule of thumb simply use either OM3 or OM4.
I would use OM4 which is not more expensive, is the latest standard and has a nice color (violet).

Important: the yellow cables are for "single mode" (laser) and can't be used for multimode.

Patch cables

Patch cables are available up to 50 m in length. Some companies offer custom lengths over 50 m with the proper plugs on both ends. The cables are either simplex (one link) or duplex cables (two links).

I would use duplex cables for connecting devices, because if you have a series of devices, then you have one link as a reserve just in case the other fiber link has an issue.

To convert a duplex LC fiber cable into two simplex leads, you simply slide off the small plastic duplex clip that holds the two LC connectors together, separating them into individual connectors.

The easy process is demonstrated in this little video on YouTube:
https://youtu.be/6Xn-NZywd7w?t=11

Plug formats

Regarding the plug format, there are the bigger SC plugs, which you find at the recording interface (not having SFPs).
On newer preamps and converters, you have SFPs where you need LC plugs.
Between the recording interface and 12Mic you need an OM4 duplex cable "SC to LC".
Between 12Mic and 12Mic you need OM4 duplex cable "LC to LC".

Example cabling:

UFXIII---SC----[OM4]---->LC--12Mic#1--LC----[OM4]---->LC--12Mic#2--LC----[OM4]---->LC--12Mic#3--LC
              |                                                                                                                                          |
             +-----------------------------------------[OM4]----<----------------------------------------------------+

In this setup you need:
2x SC to LC: https://shop.fiber24.net/FOPC-F2-O4-DX-LCU-SCU-500/de
2x LC to LC: https://shop.fiber24.net/FOPC-F2-O4-DX-LCU-LCU-200/de

RME SFP modules (Multimode Transceiver)

I recommend choosing the RME SFPs for multimode because they have the proper wavelength. If you buy 3rd party, then you have to take care to get the proper wavelength and an SFP without vendor-specific firmware. This can become tricky, as there are many SFPs out there that are for Intel, Brocade, Cisco, etc., but which would not work with RME components.

https://rme-audio.de/de_sfp-module.html

Cross-finace

As an option, you can sell the other components to cross-fund this MADI-based solution, which makes you fully independent of any network-based solution, which only adds more complexity.

Other sources of information

Excel sheet for comparing recording interfaces (except PCI/PCIe based):
https://forum.rme-audio.de/viewtopic.php?id=35156

My MADI-based setups, as an example

The blog articles contain a few pictures, also showing the MADI cabling.

1. Current HDSPe MADI FX based setup:
https://www.tonstudio-forum.de/blog/ent … tup-en-de/

2. MADI cabling UFX III, M-1620 Pro, 12Mic:
https://www.tonstudio-forum.de/blog/ent … ter-en-de/

3. UFX III-based setup with 12Mic and Octamic XTC:
https://www.tonstudio-forum.de/blog/ent … iii-en-de/

The first thing I’d try is USB from the Monitor 8 to the Mac. No additional gear purchases required. USB can handle 20 channels.