Hum starting between -85 to -80db

[Soniclife]

All the stuff bad dog suggested, plus try a single stereo amp, or even taking a single amp to a friend's who has a turntable and see if it's a problem there.

FWIW I think you're picking up mains hum from a power cord, or transformer near the TT, the cable or the amps, look at cable dressing, component positioning, and anything else you can think of.