What's your wiring arrangement? You mention the subwoofer is connected to the speakers, so I'd be particularly interested in that portion of the wiring.

Here are some thoughts: if you have a pair of computer speakers lying around, you can place them on the pre-amp outputs instead of the amp. This will allow you to test the behavior of the pre-amp outputs themselves. You can also try to remove the 12V trigger from the equation between 970 and amp by completely removing the trigger cable and manually turning the amp on. I'm not sure if either of these are applicable for your case, but they're some ideas.