I tacked in an additional 1m to ground, where the 68k, and two inputs for each channel merge. This didn't help with what we're looking for, but man, did it kill some hum! I notice no sonic difference with or without the resistor when playing a chord. (Just a quick test, but I like it! I think it'll stay there.)
I tried a 100pf across the 1m (effectively grid to gnd), no difference. I tried it on the socket to its circuits ground, nope.
Channel 2 still sounds better than 1 with respect to the RF/noise floor. Channel 1 doesn't even have a cathode bypass cap on stage 1, and it's the worst of the two channels.
I made up a little brass shield to go around the input jack and its resistors, giving it its own little grounded hut to live in. But that didn't help either.
Your suggestions were awesome, thanks!