I really don't like that mode for audio reasons, I much prefer just 2ch or a surround mode (unless the room is full of people and imaging is out the door already, then the multich stereo modes can be useful), plus that mode is harder on the amp. I assume you're using the speakers set to small in the avr so you can utilize your sub? Or are you using them full range with the LFE+Main setting? Hard to tell what level your source is but if similar to streaming on my avrs, that's pretty loud at -10 and could well be reaching the limits of your speakers. I really don't think a power amp is a solution compared to more capable speakers.....