I'll chime in.
I too was wooed by the sound of the MLs when I first heard them (ascent). It lead me from being a maggie guy to giving them a shot. I picked up a pair of SL3's (best big ML for the money on the used market, imo) and was woefully dissapointed with them.
It had everything to do with the room I had them in, which was 17'w x 24' deep w/7' ceilings. These 5'7" speakers were too small for the room!
This was a two channel setup with PLENTY of power behind them. I was dumbfounded to have a pair of beefy 10" sub-whoofers blowing at me, yet have less bass output than the 8" single mirage sub I used to have. With my musical tastes leaning towards electric jazz and jamband style rock and roll, the ESLs just didn't cut the mustard. i had to go back to a box speaker (or buck up far beyond my means for the Prodigy line) to give me the sort of dynamics I was sorely lacking.
I'm now a happy Von Schweikert owner. I find them just about as fast as the MLs were (very surprised by that), but they give me all the slam and impact I could ever ask for which is something all but the largest MLs can NOT deliver, but let me get into that a little bit.
To digress a bit, the MLs can be the best speaker you've ever heard. I'm a big fan..but there are too many extras that *have* to fall into place for them to really shine. The room acoustics and matching the panel to the square footage of the listening environment is the make or break deal w/the MLs, and w/a room the size of yours you will need the Ascents or SL3's, I would guess.
Then again, you are talking 5.1, which is an area I know nothing about. I'm sure craming 5 pannels in that room of yours will no doubt make up for the sheer volume of pannel needed to pressurize that space in a two channel stereo only rig.
final advice, consider your musical tastes, how much music vs. movies you will be sitting in front of, the size of your room, the acoustics of the area..etc, as all of these things play a HUGE roll in squeezing the magic out of Martin Logan.
Good luck!