Which to keep! Pick one of these two soeakers

Sound wise, your choice, you've go both on hand. Panels and boxes sound very different. I've had panels, electrostatics, and boxes. Set up for panels can be a journey, boxes are relatively simple. Ditto amplification. Those old spendors are a fine speaker. Panels can (can, not will automatically) sound more dimensional if properly set up. 

I'm all for using one amp for both panels and subs. I've a hard time thinking the Adcom would be a good match (soundwise) for the panels. When you set these up, I assume in a somewhat triangular configuration, you need not be as concerned with sidewall reflections (as you would with boxes, but the rear wave is a potential problem. To hear this speaker best it should be about 6 ft off the wall behind it. Dispersive material on the wall wouldn't hurt much either. Good place to start anyway. Take your time with setting up these speakers before you come to any final conclusion. 

You need a passive attenuator of some kind between your pre-amp and one of the amps, probably the amp feeding the sub. I see them coming up for sale used between $400 and $600, but from my point of view I think what you might gain by bi amping these speakers you’d lose by all the extra stuff it takes to do it. I’d run them off one amp. FWIW, the Musical Concepts mod changes my opinion of the Adcom, but I’m not convinced that it is a better amp for the panels. My gut tells me the ARC amp should go to the panels and the Adcom to the subs. When you figure out how you will get the two amps balanced, output wise, try switching them around.

Just for fun, humoring me perhaps, just try running the speakers full range with one amp. First the Musical Concepts then the ARC. Listen to the 'sound' and the differences you get with these amps. I suspect that tonally speaking there might not be a huge difference, but I think that the ARC will have a smoother sound than the SS amp. I don't know what your 'rack' looks like but you can deal with the ARC's heat by either putting it on the top of the rack or placing it on the floor next to it. For sure make sure you give the amp a lot of free space around it. 

Sell that Mac and the 555. Neither, in my estimation, has the 'quality' potential of the Musical Concepts and ARC. 

If I had your stuff and perceived problems my inclination would be to get a decent quality equalizer, like the Schiit Lokius, a six band equalizer with 2 bass frequencies, and supplement the output of the pre-amp i.e. between the pre and the amp. Costs about $300. 

BTW, are you sure that your listening position is not in a bass frequency null? If so simply moving your chair a bit could solve your bass problem. 

FWIW IMHO bi-wiring is more of a perceived benefit than a real one. I suppose with SOTA stuff and critical hearing skills the difference might be apparent, but note a lot of manufacturers have not provided for bi wiring. Some very high level stuff. The only difference when bi wiring that I could hear was when I used different cables, i.e. ones with a different set of sonic values.