That's a tall order. Looks like Infinity used their own drivers and I can't think of anything that would compare to the tweeter and midrange in the R263. Add to that, that measurements for in-wall speakers are very hard to find. If you can find a response graph of the R263 that would be a place to start. No way to audition in-walls locally?
If I was the op I’d get a wall mount and forget in walls if he’s trying to timber match a brand that does not make in walls.
Get the matching center channel and mounted above or below your screen or TV.
Find some way to make it work ..
False wall that’s about the only option if you want to timber match towers.
Or get three matching in wall speakers and use your towers as back surrounds.
Sent from my iPhone using Tapatalk