@nielso I didn't manage to get FFADO working at all, so I also have to rely on ALSA, when using it.
Hope things magically solves it selves for you!
My Firewire Interfaces have been discontinued years ago, so no Mac option for me.
I'm using a MacBook Pro 2017 simply for the reason of #RME #TotalMix. The software I use on #macOS is basically identical to what I use on Linux, it's called #Ardour. 
I don't do mixdown on that old MacBook. It's just my high-quality recording setup with the Fireface 400. There is neither budget nor a proper reason to change this. The preamps/converters of the old Fireface things are still very good.
Of course, a MacBook Pro 2017 is beyond dead for #Apple fan persons.
Concerning #FFADO, it turns out to be a permission problem.
I can
sudo ffado-dbus-server
and then
sudo ffado-mixer
And I can do stuff. Of course, for everyday use, one should configure this to work as normal (non-root) user.
When I tried back in the day with Jack and the ffado-backend to Jack, the Fireface 400 worked reliably on #Linux, but with the #ALSA drivers I'm not so sure. I had hickups and strangely it didn't sound right. But also not wrong. Or maybe my hearing got twisted on the ffado rage…