Yes, bypassing the amp is probably what's happening, and would be the cleaner way to do things. This is the exact reason I made the other thread, to get people's thoughts on whether I should double amp in order to get the volume/punch I wanted, or use the line out and O2's high gain instead.
Though I answered my own question in the end, and that raised the curiosity concerning the Vali. Without the additional gain, it can't make my 612s strong enough, no matter what speaker mode I use.
When you say 'strong enough' are you referring to volume?