Advice on brand/model of in-wall speaker for HT

I am just getting into semi-modern HT (was a 16mm guy, and still a 2-channel analog audio listener).

I would like to add rear speakers that go in-wall. I have a budget of about $350 for a used pair of rears (not including speaker cables).

My setup:
Receiver: Pioneer Elite VSX-29TX
Projector: Epson 8700UB
Screen: Stewart 110" Studiotek 130
Digital Source: Pioneer Elite BD-62FD
Fronts: Sonus Faber Concertinos (Cardas Crosslink 1S)
Center: Sonus Faber Piccolo (Cardas Crosslink 1S)

I watch mostly films from 1940s, 50s, and 60s. Most of these movies are heavy on dialogue. In other words I am not looking to rock the house with a some sort of Stallone movie.

Thank you in advance for any advice that you can pass along.

Two things to keep in mind. First, you will want to timbre match the Sonus Fabers as much as possible. Two, if your main listening position is against the back wall then an in wall mounted up high in that back wall will only confuse the sound as much of the sound from the midrange on up will pass over you and reflect off of the front wall.
Paradigm has a good range of in walls, that work really well and are showing up used or new/discounted on eBay all the time.
Specifically to your question you can find Martin Logan, Atlantic Tech, and Dayton close outs on in wall speakers here:

I agree with sticking with the same brand but at that price point there's no sonus Faber option

Finally all the movies in those eras are recorded in mono or at best stereo. So surround is less of a concern.