How to best use Magnepan MMG in 2ch/5.1 system?

You could get a great HT pre/pro and use that... that's what I did. Krell HTS 7.1 sounds amazing in stereo and in HT, doesn't decode the new formats and not HDMI, but you can run the video source direct to display or use a video processor for switching and use the 7.1-channel input from a BR player analog out. The Krell is so good, that I can't tell the difference between running my Wadia 830 directly into the amp, or running it via the HTS 7.1...

I can't speak about the surround speaker options, but I (sometimes) use MMGs with subs in my 2 channel set-up and the combo is very, very good. The trick (especially for music) is optimizing the x-over.

Personally, I'd look for a pre-pro or HTR with an adjustable x-over for flexibility and/or with Digital Room Correction (like Audyssey). These features represent 2 different ways to help insure a seamless cross between the MMGs and Subs when listening to music. Of course, DRC also cleans up response anomalies. I understand that the DRC thing is a philosphical issue for some folks - so YMMV on that one.

If you pass on DRC (or defeat it for music listening), dual subs wouldn't hurt, since careful placement of 2 subs is useful in smoothing bass response for music listening. This will lessen, but not eliminate, the benefits of DRC and allow a more "purist" (i.e. non-eq'd) signal path, if that floats your boat.

One final piece of advice re: amps (or amp section of your HTR)

More power and more current is always a good thing for Maggies.

Good Luck

Marty

Thanks for the insight, much appreciated.

I'm considering the old Rotel RSX1065 to take care of signal processing and amplification. It's quite robust (and retailed for about $2k before being updated, now much less). The rear panel has a label that stipulates 4-ohm minimum impedence...and word on the street it that it's a huge, heavy piece of equipment. I've read some stories of people running 4-ohm speakers with it as well.

YMMV, but the Magnepans image so well, I do not believe a center channel is necessary. I ran my MG-IIas on a dual-use system and then tried my MG-3.5Rs in a similar set-up. Sublime in both applications.

I would stick with one - maybe two at most - seat setup for HT/music dubties. A lot here, being critical, depends on your room layout vs setup for proper seating. If it's just one listener, you'll get the maximum sound quality in regard to tonalitity, waterfall (off-axis roll-off), imaging, etc, as the Maggies being dipoles sound much much much better on-axis. Infact, I believe the only way to listen to them properly is sitting anchored between the speakers.
I would still go with a strong solid state amp (likely 5 channel) to drive these, and maybe go with tube 2 channel preamp for all 2 channel dubties. I would probably recommend the latest digital receiver for latest processing, switching, EQ (this is very important), etc, or, better, some latest pre-pro (yeah the latest Emotive Umc-1 will be dirt cheap. Although I'm bitter on how long it's been since they finnaly released it)
Maggies are hard to drive, and a more delicate kind of speaker. I personally would cross em over at 100hz range, and use a good tight, fast, potentially accurate sub. (M&K MX series integrates well,or go with smaller woofer, sealed box designs, or some high quality woofer, and set it up well)
I would not go with a receiver, as they lack current deliver and refinement in the amp sections, ideally. Expect 50% or more better sound from outboard amps, minimum!
I've sold maggies and had em in my systems over the years. While I'm not a fan for HT dubties ideally, they offer tremendous rez and clarity for the money, is the theme with the line. If you value these attributes over brute dynamics, pressence, off-axis listenability, flexibility, and durability, then these might be for you. Again, they are placement and seating sensitive, more than others. So consider lifestyle and taste.
If you do go with this route, and take care in matching the system and setup, you will be rewarded with a great soundstage
Stay with good cables and power conditioning as well for best.
good luck