Hi Mechamilk, welcome to the RME user forum.

What budget do you have?

I would recommend an MADI-based setup. It's simple and proven and has no additional complexity in terms of the network setup QoS configuration.

In regard to support, you have one contact, RME; devices with the Dante chip depend additionally on Audinate and their firmware.

Clock synchronization and change of sample rates is easier with MADI; with Dante (or AVB), the devices cannot automatically follow a clock change and need reconfiguration of the streams, as I read here in the forum.

With 8 ADAT you mean one ADAT port with 8 channels at single speed? When using double speed, you would need two ADAT ports for connecting the mixer to get 8 usable channels.

As you want to record at double speed, there is no other option.
802 FS and UFX II would offer too few ADAT ports for expansions.

1) UFX III (USB3-based)
- 4 Mic (comparable to 12Mic) also usable as unbalanced line and instrument input
- 8x Analog I/O (converter of ADI-2 Pro)
- 2x headphone outputs, can be used as 4x unbalanced line level output
- 1x AES
- 2x ADAT
- 2x MIDI I/O
- 2x virtual MIDI port (MIDI over MADI for remote controlling RME preamps like 12Mic)
- WC
- Autoset, DURec, RoomEQ, Crossfeed, triple SPDIF
- USB3 Class complient mode
- Stand-alone capabilities

2) HDSPe MADI FX
- 3x MADI I/O (2x optical, 1x coax; coax can be replaced by an optional optical daughter card)
- 1x AES I/O
- 1x MIDI I/O
- 3x virtual MIDI port (MIDI over MADI for remote controlling RME preamps like 12Mic)
- 1x headphone output, can be used as 2x unbalanced line level output
- Newer models also support RoomEQ and Crossfeed.

With the UFX III, you have an all-rounder; 4 Mic inputs are already sufficient for you.
You only need an additional device to get enough line level ports.
RME M-1620 Pro is an excellent product offering analog ports supporting up to +24 dBu.
There you will need either a DB-25 to XLR breakout cable or a breakout console.

With the HDSPe MADI FX, you have a huge upgrade potential but need a preamp and converter additionally: M-1620 Pro and 12Mic.

For connecting the mixer via ADAT:
With the UFX III, you then have two ADAT ports free (16ch at single speed and still 8 ch at double speed).
With the HDSPe MADI FX (which has no ADAT ports), you can use the ADAT ports of the M-1620 Pro and route those ADAT inputs/outputs through 8 MADI channels (16 at double speed) that are not in use on the MADI bus.

Also useful to consider:
- ARC USB
- One of the RME reference converters (ADI-2 Pro FS R BE, ADI-2/4 Pro SE)

If you want the upgrade flexibility of MADI (or Dante), you can't use 802 FS or UFX II.
And when working at double speed, then two ADAT ports would not be enough to connect an external 16 port AD/DA converter, most interesting devices have nowadays at min 16 ports.

For comparing USB interfaces, you can take a look into my Excel:
https://forum.rme-audio.de/viewtopic.php?id=35156

That is the answer i was looking for!
Your excel file is perfect.
I will use all ADAT on 24bit 96khz so 4 channels per I/O.

Correct me if I'm wrong,
I can take the UFX III and have:
- 12 line INs
- 8 channels ADAT 24bit.
and it give me plenty of possibilities to upgrade later with MADI. 
Thank you for your reply.

Some details regarding the analog inputs:

- 8 line inputs in the back of the unit supporting balanced and unbalanced connection.
   These are the normal inputs for external devices that connect with studio line level.
   Input sensitivity switchable between +19 dBu and +13 dBu, max input level +19 dBu.

- 4 Mic inputs in the front, which can be used as instrument and line inputs, only for unbalanced connections.
   There are no fixed ref levels between which you can switch the input sensitivity.
   For this you need to use the preamp gain in TM FX, then the max input level with Gain set to 0 dB is +18 dBu.
   Maximum input level with Gain at 75 dB = -57 dBu

See the manual ch 39.1 for details.

My personal preference is to use balanced connections wherever possible.
Not only studio gear like EQs, Compressors or FX have those, also some keyboards or other devices.

The four inputs in the front I prefer for using with Mics or as Instrument inputs (unbalanced).

So much useful information.
Thank you, can't wait to become part of the RME family.
Should I expect a WOW effect the first time I hear the converters/outputs?

I'm in the music production since the 90's with an humble home studio. I had quite some good gear for the time some time ago but i didn't upgrade the sound card at the same rate i upgraded my synth army , now i have a low budget interface, and that is my bottleneck at the moment. I just can't wait to compare the difference.