Image/soundstage and punch/bass

You might consider a pair of Magnepan DWM's, about 1700 or so for the pair.  200 to 40 hz to augment the MG12's.  Add 1 sub or two if you can.  I use 2 10s and a 12 to pressurize the room about 65hz.  IMHO opinion this helps the maggies bottom a lot.

Man, I didn’t know ET was still around, let alone making speakers. I have a bunch of Rythmik subs here, but the ones in my main system--- a pair of sealed 15" are crossed over pretty low- and "punch" to me, is more upper bass, not just deep bass. How high do you run these Rythmiks out of curiosity?

Yup @whart, and ET's Bruce Thigpen is still exploring new territory. Check out his TRW-17 Rotary Woofer; output down to 1Hz!

Tekton is getting great reviews in that price range

I just finished building my own Swarm system with 2 Dayton amps and four 10" subs. Total cost including premium rosewood veneer was about $2800. Even with just a quick setup and level adjustment the bass is deeper, faster, more powerful and much more seamlessly integrated with my Talon Khorus than the Talon Roc that I will be selling. In fact its deeper, faster, and more tuneful than any bass I've ever heard in any system at any price anywhere. 

When it comes to bass its not which sub its how many. One or two simply will not do. You need four. The two amps I have is overkill, not needed for power but for greater phase control. But just the way it is now without adjusting phase its better than anyone can do any other way.

With one amp, and paint instead of premium veneer, the cost would be right about $2k. All-in. For SOTA bass. 

SOTA bass from a distributed bass array, or the same crap everyone puts up with from two subs. Your call.

Speaking of calls, if you're not into DIY (and it is a lot of work) pick up the phone and call Duke. Mine is based on the Swarm he sells for about $3k.

http://www.theabsolutesound.com/articles/audiokinesis-swarm-subwoofer-system/