I use M-audio profire 2626 with FFADO.
It have an option that can disable master volume knob in windows mixer. Also, I can select output mode for optical port "B" (ADAT or S/Pdif; port "A" - ADAT always), but in ffado-mixer I can't do it.
I found a windows PC and change this setting in windows mixer. After that master volume knob saved their settings permanently, but status of optical port mode unknown. I route an audio stream to all outputs in qjackctl connections tab, I see a signal on analog autputs, coax. output, but there is no signal on optical output "B". I know nothing about a reasons of this problem, but I suppose that we must have a control of this options in ffado-mixer at first.