This one's internal mixer can be controlled from Linux:
http://motu.com/products/avb/624
It is a bit pricy though. It does take ADAT, but does not have word clock
in. Can handle as many as 256 audio lines (128 in and 128 out with an AVB
extender or two) It says it is USB2 compliant (works with OSx in USB2 or 3
mode with no extra driver). I would try before buy.
--
Len Ovens
www.ovenwerks.net