Looking to upgrade my back surround sound speakers


I am looking to upgrade both my back surround sound speakers as part of my 5.1 setup. I currently have Martin Logan Spire as my L/R and the Martin Logan Encore as my center channel. Any suggestions? Should I keep with the Martin Logan brand...do they make dipole/bipole/monopole speakers?

I have a beam about 10 inches behind the listening area and a wall in which I would mount the rears. I prefer not to dig into the wall and thus prefer mounted speakers.
pig2fever
I figured its more about home theater since it was posted here and yes music is a different animal but even so for the 6 and 7th channels I would challenge most anyone to know the difference of a carefully chosen non matched speaker over a matched one. If budget restrains you from doing a match, dont sweat it too much is all I suggest.
I just realized that the beam is only 7 inches wide and thus your typical back surround is ~10 inches. So I am now looking into Anthony Gallo speakers. Never really heard of them. What is your opionions?
They make a fine mini monitor and for what your doing it will work fine, just make sure you set correct crossovers as they have very limited low range output.