Hi Zarabozo.

Look to my comparison Excel, Line 26 "Driver" (also available as PDF).
For USB, there are only two drivers: USB and the later MADIface driver.

https://www.tonstudio-forum.de/blog/Ent … B-MADIfac/
Direct Link to Excel: https://www.tonstudio-forum.de/attachme … 9-19-xlsx/

So, the following interfaces are supported by the same USB driver: Babyface Pro FS, UC, UCX II, 802.

I would recommend, to take another 802 because then you have the following advantages
- for Option A: the same converters with the same converter latency not to get offsets in the DAW
- for Option B: two ADAT ports to be able to route up to 16ch between the two interfaces
  without having to route through the DAW with the full RTL over USB.

There are two possibilities to connect a 2nd audio interface

Option A) Two (or more) in parallel
     - Offers two possibilities for routing channels between the recording interfaces
          - routing all channels through DAW
          - routing up to 16ch between recording interfaces through ADAT (8ch per ADAT port in single speed)
     - Best option to use even more than 2 interfaces in parallel (more ADAT ports or WC for clock sync)

+-USB----802#1 (clock master)
|                | |
PC           ADAT (clock synch via ADAT, alternatively over AES or WC)
|                | |
+-USB----802#2 (clock slave)

Option B) 2nd unit behind ADAT
    - working mainly in one TM FX instance
    - any to any routing
    - the 2nd unit either in stand-alone mode or connected to USB to be able to operate it through a 2nd instance of TM FX

PC+---USB---802#1----ADAT1-----802#2 (either stand-alone mode)
    +---USB (optional)------------------+      (or additionally connected to USB to be able to manage it via 2nd TM FX instance)

To Option A) Two or more interfaces (best of same type) in parallel

According to the manuals, RME supports officially up to three devices (of the same type).
Even more should be possible if the computer allows it performance wise (number of channels).
They should be best of the same type so that the AD/DA converters have the same latency.
This is important if you have a setup, like in Option A, to not get track offsets because of different converter latencies.

You only need to take care of two things:
- to clock synch both devices by either WC (Word Clock) or by using a digital connection (via SPDIF, AES, ADAT)
- Windows: in the driver settings, you need to use the same ASIO buffersize. Otherwise, you get track offsets by this.

If you want to route audio channels from device #1 to device #2 you need to route either in the DAW (with the RTL through USB).
Or you have to use the 1 or 2 ADAT ports to route up to 8/16 channels between the two devices.
Alternatively, choose option B), then you have any to any routing in the TM FX instance of the main unit.