Whoa!! That's not how I would use tone control.i switch amps quite often so I'm not sure if the terminals are the issue. I have tried both bi-wiring them and otherwise but haven't noticed any difference. Another thing of note is that the PM6006 is better at deep and loud bass than the SR6013 when you use the tone controls. The bass response of the Evo 4.2s become phenomenal and almost floorstanding like when you increase gain on the bass to the max.
Ideally, there should be no need to tinker.
If the need arises, it would be a couple of notches up or down depending on content/track
Cheers,
Raghu