Just to add to what XEagle Driver said - for a HT setup, I would NOT go with in-ceiling speakers for the left, right and centre channels. You could go with in-ceilings for your surrounds, but free-standing speakers are best for every position. My ears aren't as discerning as some of the guys in this forum, but I do know one thing, in-ceilings for a HT or a 2-channel system are a severe compromise. If space restrictions or WAF dictate that the speakers be hidden, in-wall would be a better way to go.
For the best sound, your speakers should be pointing towards you, not the floor. In-ceilings are only good for "ambient sound", to which you won't be paying close attention.
Would I be guessing correctly, that you are thnking of in-ceilings because the attic is above and access will be easier? If that's the case, don't take the easy way out! In-walls can be done, but it'll be more work and more mess. The results would be superior though.
If you don't want to go that far, I would suggest that you go with free-standing speakers over in-ceilings. I put speakers in my kitchen ceiling, only because there wasn't enough free wall space. They're only good for ambient sound in that position, but in the kitchen, that's good enough. For a HT that will not be good enough.
