For those following this discussion, I finally got my new amplifier, too. A Jensen 50wRMS x 4 thingy. This single amp replaces two separate old/cheap/crappy amplifiers with the single amp.

All ground loop problems have gone away and the whole system is very quiet now (and can also get a lot louder now).

I think this is due to a few factors: 1) Higher quality (more expensive) amp means better noise isolation and grounding circuits designed into the amp itself. 2) More amplifier power means that your amp's gain controls are turned down further when everything is properly adjusted, reducing the noise floor even more. 3) In my particular case, I reduced the number of components plugged into the same audio chain, so that's one less device to induce a different ground potential into the mix.

So if anyone out there is having noise issues, definitely give your amplifier a close inspection and see if it's really up to snuff!

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Tony Fabris