Congrats on the great used deal on the R500's!
Actually it looks like the drivers for the R500's and the R200's are identical - the R200c will probably be an excellent match.
I wouldn't worry about dipoles for surrounds. If your listening is primarily stereo music and HT/TV you can probably get away with Q series speakers as surrounds (Q100 or Q300). If you listen to a lot of surround music/concerts you should probably stick with an R series speaker for surround (R100?).