MBL Fronts and Center - need rears - ADVICE PLEASE

I have a pair of MBL 101D's and a 121RC center channel up front but no room for floor standers in the back of the room for the surround channels.

Can anyone recommend an in-wall or on wall speaker that will be a good timbral match to the MBL's? I know they are only surround channels but I listen to a lot of Multi Channel and Trifield surround music and want a pair of rear speakers that can run with the pack :-)

Thanks in advance!