No Adat, no Totalmix, the toslink socket can transmit a stereo SPDIF signal to another stereo converter DAC.

Tee, the ADI-2/4 Pro SE's product positioning is "reference converter".
You need to get a "recording interface" to get TotalMix FX and then select a model with the needed I/O ports and features.

The ADI-2/4 Pro SE you can integrate into the setup like I described here in my blog for the ADI-2 Pro FS:
https://www.tonstudio-forum.de/blog/Ent … our-Setup/

Regarding I/O ports: "2-16 or so IO" is not very specific. You also need to tell, whether you intend to work at single or double speed?
Just in case you do not know: ADAT protocol has 8ch@single speed, but only 4ch@double speed (2ch@quad speed) due to channel multiplexing to get more bandwidth for double (and quad) speed.

Depending on your demand (number of channels and sample rate) you need to choose between a solution with 1 - 4 ADAT ports or even a MADI based solution.

The prices and features of the devices are different (starting from €444 for a Digiface USB up to €2649 for an UFX III).

Depending on the devices that you want to connect you might also need to take care of, that the recording interface supports WC (Word Clock) for clock distribution, this gives you more flexibility regarding the placement of the "clock-master" in your setup.

Also important to know whether you want or need something USB based or whether it may also be PCIe based.

So please be more specific and give some additional information about your requirements, thanks.

A new interface, something like the UCX ll or Babyface Pro FS, those have superbe AD/DA, normal people will never hear a difference to the ADI-2.
In your case I would use one interface (UCX ll) only.
For using interface and AdI-2 together both connected via USB it is usefull to create an aggregate device in the Midi-Audio-Setup.
Better connect only the interface via USB to the computer and connect the ADI-2 via SPDIF to the interface. See post 4 integration blog article.

Usually you wouldn't need an aggregate device:
- You would buy a recording interface to get TotalMix FX.
- Then you add converter or preamps via ADAT or MADI to the recording interface.
- Next, if you want the ADI-2/4 Pro SE as reference converter you would connect it to the recording interface as well.

4 Stereo Channels means 8 analog I/O channels in total.
But you still didn't mention the sample rate that you intend to use.
For normal applications, home recording, single speed (44.1/48 kHz) is still enough.
Then you can connect a preamp or AD/DA converter using this one ADAT channel.
But if you should intend now or later to work at double speed (88.2/96 kHz), then you would need 2x ADAT I/O.
For connecting the ADI-2/4 Pro SE you would need another I/O port, either AES or optical/coax SPDIF.
I would recommend AES or optical I/O to also get galvanic isolation between the devices.

You could also think of getting a larger interface which has already 8x analog I/O and using the ADI-2 Pro for monitoring.
The analog I/O ports are fix and the number of channels do not change with the sample rate up to 192 kHz (quad speed).

But here I would also like to question what your maximum budget is.

You could get something like Digiface USB or RayDAT plus reference converter.
But it would also be possible to get an UFX II in combination with ADI-2 Pro.
Then you have already 4 very good Mic preamps with 75 dB gain, compareable with the 12Mic.
And you have 8 excellent analog I/O ports with the AKM converter from the former reference converter generation, ADI-2 Pro FS. And not only that but all the advanced features like: Autoset, DURec, RoomEQ, Crossfeed.

What applications do you have? I would strongly recommend to work with TotalMix FX when doing recording.
It gives you an excellent flexibility in terms of monitor mixes and routing capabilities in general.

If you do not need the special features of the ADI-2/4 Pro SE (connecting turntable, 2nd playout path), then you can save some money by getting an ADI-2 Pro FS R BE and then to go for the UFX II.

      +---USB2---ARC USB (optional: nice remote for TotalMix FX)
Apple---USB2---UFXII---8x analog I/O
|                                 ---2x ADAT (both ports switchable to optical SPDIF)
|                                 ---AES-------------> ADI-2 Pro FS R BE ---1/2 active monitors
|                                                                      |                       3/4 headphones
+---(*)USB2------------------------------------------+

(*) USB connection only for firmware updates and to remote control the ADI-2 Pro using ADI-2 Remote Software)

With the UFX II you have still a reserve of 2x ADAT I/O so that you could add either preamps and AD/DA converter at single speed. Alternatively: either Mic Preamp or AD/DA converter at double speed.
Cost: €2099 + 1699 + 159 ...

Hi again, do you think the RME Fireface UCX II could replace my 2/4 Pro SE? Which chip does it use? Comparable sound?

At the moment, I have my external EQ, compressor wired in perfectly with my 2/4pro se for computer output monitoring and when needed, daw insert/loopback recording and monitoring of my analogue gears incoming signal. I would just like to add more channels. Do you think UCX 2 or baby face pro fs which could act like arc?

Thank you! I will investigate further on your suggestions.

Yes good point. I am thinking UFX2 or maybe even 3?

I wonder..... could an Atmos rig be run from the UFX3?

mmmmnnnnh tempting. Maybe I should buy that and sell the 2/4 pro SE....

Are UFX III and UFX II identical in terms of converters, preamps etc

The UFX III got the facelift and then a little later the UFX II got the changes as well.
UFX III is the "leading platform" here. Now UFX III and II are equal except USB3 and MADI.

As this is now the interface for many years I would invest into the UFX III to get MADI.
More headroom and if you would need to buy the UFX III you would also have to completely redo the TM FX settings.
Then start better with the UFX III.

Question is whether you perhaps might want to keep the ADI for its special featureset.

> I love the sounds of the 2/4 pro SE, but do not need the turntable option. Does it have more "special" featureset than this?

Pls compare manuals, a brief overview here in this sticky posting:
https://forum.rme-audio.de/viewtopic.ph … 06#p165706
and here in my blog:
https://www.tonstudio-forum.de/blog/Ent … ses-EN-DE/

The sound differences will be small as RME follows a high quality transparent conversion.
But there might be some differences at single speed.
The UFX III has the converter of the older model ADI-2 Pro FS R BE which is excellent for a recording interface.
But there is no possibility to switch D/A filter, this is a feature for the reference converter only.
This might be interesting for playback, see one of KaiS postings that the ADI-2 Pro FS Slow Filter was a little better for locating percussive instruments in the soundstage.

The ADI-2 series of devices has auto reflevel as a feature, very interesting. I just uploaded and Excel where you can see over which wide volume range the SNR/Dynamic is being kept in the optimum area.

Then you have lots of useful features like dynamic loudness  and a state overview for troubleshooting digital connections.
Also a SRC (sample rate converter) and the so called Bit test to make an end to end check from player to DSP whether your audio path is lossless.

The differences / features of the ADI-2/4 Pro SE you can see in the Excel list of the sticky article.
The ADI-2 Pro FS R BE would also do very well.
The ADI-2/4 offers a little more: 5th reflevel, pentaconn plug for balanced phones, turntable, RIAA, on the back TRS 1/2 instead TS 1/2 and the 2nd DAC can be used for that channel so that you get an independend playout path. A wish from mastering engineers. But you have enough analog channels by the UFX III ...

No night and day differences, but some little differences. Instead of loosing money by selling and buying new I would keep the ADI-2/4 Pro SE as you have it already.

No you didn't.