I have a house full of Polk in wall/ceiling speakers, LCs and TCs, for my whole house AV system and love them. They handle bass nicely, mids are smooth and the highs are not to bright. I bought mine on eBay and saved a ton of money.
I would buy an actual rack, a rack that you can physically rack mount gear into and install that into your opening. Then frame it out from there and all should be good. But that is just me, spend a few bucks to relieve a future headache.