Best REL Subwoofer for Magnepan 3.6's

I am considering trying a subwoofer with my Magnepan 3'6's. The REL subwoofers seem to be highly praised and there is a decent supply of used ones available. What are you recommendations for the best REL to try? My room is fairly large at 17w x 26L x 9h.
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.
Much Thanks! Scolley-

REL makes the finest sub on the market. One would be hard-pressed to find a better sub. Ease of use, ease of system integration, excellent dealer/retailer network and an outstanding product line makes for a no brainer choice. Even the older series subwoofer(s) are never out of date IMO.
Happy Labor Day!
After an number of months, I made a pretty big change that I thought was worth reporting...

Setting the RELs up initally sounded good - using their recommended front corner placement. But after months of listening, I became convinced that my bass was not quite as tight as it should be. And was - at times - a bit boomy. The fix was really easy.

I merely moved the subs out of their corner orientation, to being in-line with the plane of the maggies, right next to the woofer side of the speaker (opposite side from the tweeter), center of the sub on that plane. Audible difference. Nice, tight, coherent bass. Not remotely boomy. And any slam is now more crisp. It's a difference that you can literally FEEL. :-)

Obviously this completely ignores room modes, so your mileage may vary. But the maggies' bass (withot the RELs) sounded good where they are. So it's no surprise that putting the RELs right next to them would sound good too.

As stated in my first post, I've got 2.7QRs, not 3.6s like the OP. But I'd be shocked if REL T5s did not work great with them too.

FWIW my crossover is set to around 50 Hz, using high-level inputs at ~ 25% volume on the RELs.

I had the same type of success with a pair of JL audio E112 (with thiel 2.4). I use their built in high pass crossovers between the pre-amp and amp and it sounds great. The key to using subs is a good high pass crossover. I will be using subs on all my systems going forward. I crossover at 60hz but with the crossover I can really blend it anywhere between 100hz and 30hz if the gain is set right in the subs.

always nice to read about another Thiel speaker owner.
What brand(s) of other gear is in your system?
Most important, want brand(s) of cables/cords is in your system? Keep me posted & Happy Listening!