Any suggestions on a conventional box speaker to act as center for a pair of MMG fronts? I don't have the space for a Maggie center (nor budget). Thanks.
I don't recommend running a box center with any Maggies. Sticking with Maggies all around is your best bet if you like the planar sound.
To do so on a budget, consider: 1) Running in phantom center mode; move the fronts closer together if possible to close up any center hole in the soundstage. This shouldn't cost you anything! 2) Keep an eye out for a used MGCC1 or MGCC2. They're going for about $350 on Audiogon right now. They have very limited bass, so make sure your receiver / processor can cross over at 150Hz and route all lower frequencies to a sub or the mains. You're right that the MGCC3 is expensive at nearly $1,000. 3) Get another pair of MMGs ($550) and use an MMG in the center. (Your setup would need to be able to accommodate a vertical floor-standing center channel.)
Since I posted this a long time ago, Magnepan has since introduced a low-cost center, the MMG-C. It lists for $349. Usually sold to accompany the MMG-W wall-mount speakers, it can also be used as a separate center for Magnepan home theaters based on floor-standing MMGs.
It's still bandwidth-limited, with a -3dB point of 100Hz. But that's actually more mid-bass response than the original MGCC1 (which I have) and MGCC2. That's also a more accessible crossover point for most receivers - so I would think this is a better choice than the MGCC3 to match with the MMGs. The MGCC3, being more expensive, has an 80Hz -3dB point and more detailed / high-quality sound. It would be a better choice to match with the larger Maggies (1.6/1.7, 3.6).