What's powering your Maggie OnWalls?

I don't want opinions or conjecture, just hands on experience.

What pre/power, HT recievers are the folks who own Magnepan OnWalls using?

My surround system is far more modest than the two channel. The Outlaw 950 Surround Processor feeds a Rotel RB-976 six channel amp (configurable 6,5,4,3 channel) for the 7.1 HT system. I run five channels of the Rotel; one bridged for front channel and four to respective L/R mids and L/R rear surrounds.

My experience? I know it's nowhere near SOTA HT sound, but my priority was economy, realiability and decent sound. It has met all those criteria. In the HT at times I have mixed dynamic (main/center) and planar (surround) speakers without shame, which is poor form for top end HT rigs. However, I watch perhaps one movie per month; at least 95% of the time I'm listening to the two channel rig. I swap panel and dynamic speakers as my mains in/out of the rig, so at times there is more or less consistency between the mains and the rest of the 7.1 system, but I have accepted this as part of the price of directing the bulk of my funds toward two channel. It's good enough performing that I have never been distracted from a movie due to disparity between the technologies such as macrodynamic imbalance, tonal variance, etc. in the sound.

Given my criteria and current use I have felt no need to upgrade the processor or the amp for the speakers. If convenience/cost/low heat is the primary concern I would recommend you look into Class D amplification. If sound quality is paramount then perhaps you should prefer Class A/B.
I currently run two Magnapan MC-1's on wall as rear surrounds. My pre/pro is the Arcam FMJ-888 and the amp for the center and rears is the Odyssey Audio HT-3 that I had Kraus upgrade to his Kismet reference line. I am running a 5.1 setup.

To be very honest I am extremely satisfied with the musicality and sound effects coming from the Maggies. The combo of the Arcam and Odyssey is a perfect match for my system.