FWIW....2cents at least...
I bought a Lucid GenX192 several years ago to answer all those same questions I had at the time. I did several tests, with the DM slaved to the GenX and not, both playback and recording, and there was practically no difference. No extra clarity, no change in imaging, and no magic "unveiling" of a fancy new sound. After reading the info from George Massenburg, I really felt there was no reason to slave to the GenX. And, I became convinced that the device doing the A/D conversion (my 3200 in this case) should be the master clock. But, I keep the clock in my rig to distribute the DM's word clock to other digital devices, so it still has its use. But, I do try to keep all conversion done within the DM. There you go.