Magnepan mg1.6 vs mg1.7 bass quality?

Lecram, based on your stated preferences I'd say either go all the way up to the 3.7R's or else add a sub to your 1.6's. The Rel R-328 or R-218 mate well. Also, I'd suggest staying away from silver IC's etc. Stick with copper.

I auditioned the 1.7's about a year ago, and owned the 1.6's at the time. It was a brief audition, because I was really interested in the 3.7R's which I bought. That said, the 1.7's did not strike me all that favorably. I would say, though, that addition of a REL 328 to the 1.7's made an amazing improvement. Completely changed the tonal balance in a very good way.
So, you might want to consider sticking with your 1.6's and adding a sub. Another thought would be to go to a warmer, softer amp. I've just never bought into the maggie/bryston pairing.

Lecram, I never had the opportunity to hear the 2.7's, so I don't have that as a point of reference. I agree the 3.7's may be a stretch in your room, but mine are in a room 15 x 19 x 8. Take a look at my system pictures to get a feel for how they look. The funny thing about the 3.7's is that they integrate with the room MUCH better than the 1.6's did. I was able to take most of the room treatments out of the room.
I'm not a huge fan of Bryston and Krell amps with Maggies. I do like the SS Cary amps (obviously), so you might think about that as another way to warm things up a bit. I still think the best move is to pick up a nice REL sub and see if that gets you where you want to be. You can snag a used R-218 or R328 pretty cheaply. Even cheaper if you go with an older REL.