You may have already done this, but I'd suggest the following tests.

Let's say the left speaker is out. I'd try a couple of tests. First, I'd connect that speaker to a different channel on the amp (left surround channel, for example). Make sure the channel in question is hooked up and turned on at the 970, then play something (a test tone will do) that uses that channel. If you get sound from the speaker when it's on the left surround channel, I'd move the left pre-amp output from the amp's left channel to the left surround channel (which the speaker is still connected to) and try playing something again. That will test all of your variables: pre-amp output, amp channel, and speaker.

Also, take a good close look at your speaker wiring - make sure no strands have gotten loose and you're not shorting the positive and negative leads together at either the amp or the speaker.