So I reran all the grounds so that the amp/line-converter/inverter were all grounded to the same point.
Still had a little hiss, but not nearly as bad, though now the touchscreen had [b]a lot[b/] of static.
The headphone jack wasn't quite as bad either, still no sound making it to the speakers, but it wasn't installing killing it when unplugged.
So I throw a hailmary and pick up a ground loop isolator from RatShack.
Everythings golden (except using the built in dock headphone, maybe it was damaged the first go around?), even stranger, I was getting a problem previously that I had attributed to me screwing around with X. The sound card would be blocked on X loading and I had to reload alsa to get it to unblock. This only started happening during the install. Never happened in the house.
This no longer happens. WTF?
Oh well, problem solved, but I'm still confused.