Hi Cyril,
I used Jay Bascal's tutorial of The Rite of Spring - Part 1. I didn't change the tracks from the way Jay had them and thought it would be a great sequence to check out thru-put and memory performance.
I'm ok using Cubase and VE-PRO combination. Works Great!!! I did try the ADAT approach you are speaking of but using the in/out of my Apogee Ensemble sound interface. Unfortunately, there were clocking issues that cause cracking with just one instrument count.
The truth is that I was shocked after setting up VE-PRO and Cubase with Jay's tutorial to find out that trying the same setup in Logic 9.1 and the new VI-64, that the Logic config wouldn't even begin to play (with just empty instrument interfaces loaded - no sounds, blank tracks and no effects). We are talking just tracks with VI loaded in them. My thoughts are that the VI interface's performance would be the same whether in VE-PRO or Logic and the only difference being the host. Maybe someone from VSL could confirm. I remember noticing a performance improvement when I was comparing Logic to the original Vienna Ensemble using the same sequence and instrument count. There was a very noticeable difference in CPU usage back then.
Without doing major research on the subject, it just seems in my limited testing, that from a thru-put perspective, using VE-PRO to host VI Instruments is the way to go. I guess a real good check would be to set up a medium sequence in Logic using VSL and maybe some other libraries and then take the same configuration and use VE-PRO as the host and Logic as a sequencer only leaving Cubase out of the picture. Maybe time permitting.