you can’t control two EQs on separate channels simultaneously on the OT itself. (sigh, OT OS feature request no.789: assignable encoders - but see bottom of post too)
ofc you can mix in a track without bass, take out the bass on the old one, then go back to the new track and bring in the bass. but that always leaves you with a ‘basshole’-cheapo-kind-of-mix.
you could also try mapping the eq bass band levels to xfader scenes, but that’s always turned out kind of lame for me, as you lose energy at the center position of the xfader, no matter how clever your XVOL+XLEV transition curve is.
if you don’t mind hooking up an iphone via midi interface, you can use my MMP patch ‘octahack’. it has a subpatch where you can map the OT’s MIDI channel encoder pages to whichever internal parameters.
alternatively, use for example, touchOSC on ipad to make a custom control surface. or a sufficiently programmable hardware midi controller.