Suggestions for a rear surround for VS speakers

With that amp I would look into source technologies. www.sourcespeaker.com. I own cinepro amps and there is no match better then Source.

If it were me, I'd get two more TS150's! You will have a hard time finding anything with that speaker's frequency response, dispersion flexibility, and timbre matching capabilities. And size wise, it's pretty low-profile too!

I have the same front setup as you, and when my thoughts turn to adding channels 6 and 7, they turn to thoughts of VR-1's. Or TS150's. Or, if "profile" is a paramount concern, something like the Era Design 4, which could possibly be wall-mounted (although it might prefer a little more air around itself). But at least it's tiny. Would have to transfer the low freq's to a sub of course.

Good luck with your quest. If you find a good in-wall match, let us know.