Looking to upgrade my back surround sound speakers

Dont get crazy on this idea of voicing for rears surrounds as noted its not exactly in your face sound. The content will be ambient, add space and depth with some affects mixed in. There is no need to be anal about them, as long as they are in the general ballpark you will be just fine.
I used B&W surrounds with Innersound Eros so I speak from almost exact experience. Also at that distance its questionable as to the need at all but I would do it if thats what you want, just place them high on wall so the dont call placement attention to themselves.

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.

In 10 yrs we are going to be listening to 50.8 systems lol

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.

Oh you called them back surrounds and that usually means the 6 and 7. Typically they are called center rears or surround backs.
For the 4th and 5th speaker you need to be a bit more careful in selection. Maybe the Gallo would do a fine job if its just for movies.