Speaker problem or receiver setting

[ArkGuy]

My initial set up for my Onkyo 705 and three fronts worked fine: L/R towers running through a two channel power amp and then to the receiver's pre-outs for those two channes. The CC was plugged directly to the receiver. Life was good for a couple of months.

However, yesterday there was no sound from the right front. Left and center were fine. After checkng all the connections and powering things up I smelled something bad from the amp and could tell it was really hot, much more than normal, so I shut everything down.

After unhooking everything from the amp and plugging the left and right speakers directly into the receiver, the center channel continues to work fine. However, now the left and right sound too quiet, like the sound is only coming from the tweeters, plus the sound from the left is distorted.

I've run the set up program again, I've manually checked the speaker configuration, and I've rechecked every place a wire goes into the receiver or the two misbehaving speakers. I brought one of my old Bose 301's out of mothballs and plugged the left wire into it and it seemed okay. I'm at a lost as to what to do next.

Short of boxing up the speakers and taking them to a repair shop, what else could I check?