I am testing the use of my Emu 0404 USB interface as a standalone A/D converter, bringing the digital signal into my new UFX via AES.  I may need to do this someday to add a couple extra inputs.

Using a pair of matching SDC mics, I connect one mic mic>UFX pre (ch 9) and I connect the other mic mic>Emu pre> Toslink output >UFX ADAT2 input via AES.  I have a Toslink cable from the UFX ADAT2 out to the Emu digital input and the Emu digital output connected with Toslink cable to the UFX ADAT2 input.

I get “Lock” light on the Emu and a "Sync" indication on the UFX.    In UFX Settings, I have 48 samples set for the buffer – FYI, I have been successfully recording 6-9 tracks at once with this setting.  AES input is set to ADAT2.

As I record my voice into both mics at same time and playback both tracks together, listening to both tracks at same time with headphones, I hear odd sounding playback, as if one track is slightly out of sync.  In fact, if I nudge the first mic track in my DAW 4-5ms to the right (add delay relative to the second track), the signals from the two mics seem to match up and it sounds good – about as good as if I use two analog inputs on the UFX.  Individually, each track sounds good – but when they are played together, it sounds pretty bad.

So my question is, am I wrong to expect the playback to already be synced up?  What exactly is the clock sync doing if not getting these two tracks to line up?

Is it normal to have to nudge tracks when using external A/D inputs into the UFX via AES or ADAT?