Updating this discussion for those that might still be interested in such a pairing...
My music only listening room is 22' wide by 25' long with an "A" shaped vaulted ceiling 8' at the lowest, 13' at the peak. A decent amount of air to energize.
I've paired a set of two REL T-5's to my Magnepan 2.7 QR's. T-5 crossovers set at around 75 Hz, level 50%. Using the T-5 "High Level" inputs. Subs pushed into the room's front corners behind the Maggies, roughly 4" from the corners.
Have never used another sub. But IMO this combination, in this room is spectacular.
The 2.7's are authoritative enough on their own to not require a lot of supplementation. And the pair of T-5's combined have power in reserve - neither being strained at all. And the results...
Well, all my musical vocal and acoustic instrumentals are just as transparent and precise as they always were (gotta love Maggies). But now Peter Gabriel's Sledghammer has got that SLAM that I've been missing. And the drums on Patricia Barber's Too Rich For My Blood have the percussive power that I've always known should have been there.
I cannot say what this pairing on a classic 2-point series Maggie means for people with the current 3-point series. Though I'm sure people more informed than I about the differences should be able to speculate.
Hope that helps. :-)
PS - One last point... They were super easy and forgiving to set up. On day one I tossed them in corners, and tinkered with placement, crossover point, and amplification level for about an hour and was very happy with the results. Later, I spent many hours measuring dB, listening, recording, comparing, making incremental changes... you know the drill. Anyway, at the end of many hours work, the ideal speaker positions, crossover point, and amplification wound up so close to my original 1-hour assessment, that the difference barely matters. It's subtle. A pair (in my room, with my equipment) is that easy to set up.