Same issue here, no answers for any of us it seems like. Running 2 FireFace 800's through adapters, and independently, they both work fine. But the second you try to use them as an aggregate audio device, it just crackles and sounds demonic. I contacted Apple Support and they gave me the normal NVRAM / Apple Diagnostics run around and disconnected on me. Really annoying. I would really like to use the new M1 Mac Mini I spent a good deal of money on for my recording sessions, but I need both interfaces in order to do this with my workflow. Although the M1 is very fast and has a lot of pro's, it seems like they forgot to perfect the Core Audio or something with the software. RME released a driver for a 15+ year old product, but Apple seems more interested in shelling out new products to sell when they haven't even fixed the issues with the old ones we already bought. Very strange since musicians are a huge chunk of Apples demographic. Very disappointed that this seems to have no fix.