I'm actually looking at the Apogee AD16 and DA16 units. They seem like a great converter upgrade, and some people I've talked to like these better than the Digi 192 converters. The Apogees will take AES, Lightpipe and TDIF.
Have a look at RME ADI8-Pro's. If you get an ADAT Bridge for your Mix system you can tap a couple of these on the back to get 16I/O's. There's a good technical review comparing them to AD8000's on:
So, what about those German converters??? They're $700 euros for 8 ch A/D/A... the price is excelent... how about the sound quality? It is spec wise rated under even the RME stuff...