RME Babyface in CC mode with SPDIF in - XRUNS!

[rugubara]

Hi,
I'm able to use my RME Babyface as 2 in/4 out config (i.e. using internal clock, no optical input connected) at clocks up to 96000. Recently, I needed 2 extra mic inputs (4 in total). So I dusted my old M-Audio FW410, set it up for the internal clocksource of 96000, hooked it to RME Babyface optical in. Babyface reported a successful sync (sync led was on).

When I run jack, I heard the crackling sound and noticed xruns in the output. I clocked the pair down to 48000 - still XRUNs. Only when I clocked down to 44100, I could get a stable set up. I gave up my attempts to stay within 5 ms of latency and turned my frame size to 2048 - still get XRUNS above 44100.

The other way round, RME Babyface synced to internal clock, SPDIF out hooked to M-Audio FW410 SPDIF in, I could achieve stable system @96000 using ffado backend.

I was thinking about buying an ADAT 8-mic preamp (Focusrite OctoPre or RME OctoMic) for my babyface, I wonder if it would exhibit the same strange behaviour.

If anybody has Babyface with some ADAT preamp/AD, could you share your experience if Babyface in CC mode can operate with 8 ADAT input channels?

Thanks