I have an iMac late 2015 (intel) and a macbook Pro (mid 2015, also intel). I have updated them both to Big Sur from Catalina.

I connect a Fireface 400 via official apple thunderbolt-to-firewire adapter. This has always worked (although I had previous trouble with getting RME driver installs to "stick", I always found workarounds)

First the macbook pro: after updating to Big Sur, the RME stopped working. Updating to the latest drivers (driver_fw_mac_341), the fireface is recognized again. Works fine now.

Now the iMac: Updating the drivers (driver_fw_mac_341) does not fix the problem. The "host" light stays red on the fireface, the interface does not show up in my iMac sound preferences. Fireface Settings doesn't boot.
It does seem to be connected, when looking at the System Report (see picture).
https://www.dropbox.com/s/v8yvu3x0ll139 … 7.png?dl=0

When I hot swap the cable to the Macbook, this works fine (red Host light dissappears, I get audio). Switching it back to the iMac, still doesn't work (red host light, etc).

I have tried a lot. Reinstalling the drivers, giving access in Security and Privacy before rebooting, trying an older driver (driver_fw_mac_336). Deleted all RME apps and preferences, reinstalled again. Even tried copying the apps and preference files from the macbook to the iMac. Tried booting in "recovery mode" but I don't get the relevant options in Startup Security Utlility (because I'm on Intel maybe?)
Nothing seems to work.

Tested another interface (Maschine MK3) on the iMac, this works fine.

Any help is appreciated.