I'm wondering if I don't have a good enough ground. Here's the problem. With the engine off, I am reading ~12v to the dist block, and both amps terminals. If I turn on the radio,, it drops to ~6v at those points. If I remove a remote wire from one of the amps, it goes to ~8v. What's going on?

 

if your unsure of a ground, just redo it.
ground wire should be same thickness as the power wire and the surface should be stripped of paint to be safe. i usually dont use a bolt but rather use some self tapping screws

 

Sounds like a bad battery to me, I'd get it load tested.

 

Thanks for the tips. Checked everything. I bought a new battery recently so it wasn't that. It was a bad ground. Everything sounds great.