I have a Legacy LA770 500WX2 CH amplifier with two Memphis 12" subs. The amp will power on and everything, but I have no sound out of the subs. I've tried so many things, different RCA cables, different ground, and everything. The biggest thing here is that I hooked up the subs to another amplifier and they worked fine, they hit hard and everything. I had everything set up the same. So what is my problem?