Best non-Magnepan rears to mate w/Maggie fronts?

"Here's my solution: Realistic Lineaum Pro LX-5's if you can find them."

Lol. That is a good one!!
Ah yes, the mighty Lineum LX-5! A fun little cheap speaker, indeed - a big little soundstager, it is. (although dry and bleached sounding on top end, to be true, and with poor bass)
My suggestion is to forget the rears, and stick with your mains up front. Then, if you do get around to using MATCHING maggies in the rear, DO THAT!! Anything else is going to sound different, period.
If you just can't stand not haing rears, then any higher priced in-wall/in-ceiling speaker will fill in the back.
Just make no mistake about it. Nothing is going to sound just like your maggies, for certain.

95% of EVERYTHING else.

Perhaps asked a different way: anything to avoid that might not mix well with the Maggies?

Eminent Tech monitors

Here's my solution: Realistic Lineaum Pro LX-5's if you can find them. The tweeter in them may actually match the feel of the MMG with a wide soundstage? Very clean, crisp, not harsh and very wide dispersion. Cheap too.

Would love for them to be $300 or less, for the pair. They will be wall mounted.

Wall mounted? Stand mounted? Bookshelf? Price range?

Look at the new Martin Logan Motion series. These are really nice sounding.

http://www.martinlogan.com/motionSeries/index.php