Did you ever find your fix on this? It could be an amp component failure that damaged your speakers. That happened to me recently (not an Outlaw amp). Try switching the front amp outputs to the rear speakers - if you still get the low sound then the speakers are probably damaged. So the question is then what damaged them, and most likely it was the amp, which is probably also damaged in those channels. So also try switching the amp rear outputs to your front speakers, which you know work - if no sound then the amp is also bad in those channels.

Dsmith