@Naturligasteg
You may have several RME devices in TM and switch between them. I do not know if there is limit, but I have three RME devices in TM working at the same time. And TM shows even the old that I have used and do not use anymore...
RME manuals say that up to three RME devices may be used at the same time. It seems to me that it applies to driver, so if devices use different drivers it is probably more.... And someone on this forum said that 3 is tested amount and more devices may run, or not...
I do not use it and maybe I am not right, but I think one may open two instances of TM with different RME interfaces choosen. In that case one could see and operate/see more than one device at the time without switching device in TM. I am not sure about thi, one would have to try... I do not have TM at hand to try right now...
But in DAW/computer you will see all interfaces (that use the same driver) as one group. At least on Win. I guess, it should be the same on Mac. So, most probably no need for agregate device on Mac. But, Mac user would have to confirm it, if it is not mentioned in manual.
As already mentioned, if not using ADATs you may get preamp with AD and ADAT outputs and get up to 16 more channels (at 44/48 kHz). Would be probably beter than one more 802.
I did the same. I have FF 802 and RME Octamic II preamp.
Back to TM. I use FF 802, FF UCX and Digiface USB at the same time and no problem.