if you are using your system for movies, the surround audio tracks carry far less information than the front 3 channels. The "positional audio" in the surround tracks can be carried by any decent speakers, so I suggest you try your existing surrounds with the new front 3 and see if you like the setup before spending money on speakers you may not need.
If you must go to in-ceiling speakers, make sure they have rotating tweeters so you can aim them towards the listening area, otherwise they will just down-fire towards the floor. In-ceiling units from Parts Express have served me well for installations for in-laws, without breaking the bank.
