I have a VTL 2.5 and use a surround processor/preamp connected to the processor loop on the VTL (HT bypass). The VTL needs to be on to pass the front channel signal to my speakers. I think the 5.5 operates identically except, of course, it sounds a little better than the 2.5. This isn't a bad thing, IMHO, since the signal goes from your processor and then through the VTL's tubed stages before going to your amp. The sound is better than straight from my processor to the amp on my system. Hope this helps.