DrGerm, (ID Guy, by chance???
Your instincts are correct. Mounting the front soundstage in the ceiling would be a highly compromised design. Think of in-ceiling speakers like spotlights. They both shine a cone of light or sound down from the ceiling. If you are standing underneath them, you'll get great light/sound. If you're outside the cone's dispersion pattern, you get a dimmed light, or a reduced sound.
The further issue with sound is that higher frequencies are more focused and directional than lower frequencies. Therefore, the higher you go in pitch, (frequency), the worse the problem becomes. What you end up with, sitting outside the in-ceiling speaker's downward cone, is pretty good mid-bass, recessed midrange and completely missing treble.
In addition, consider that the front soundstage should "lock up" with the front video image. You want the voices to sound like they come from the speakers' mouths. If the voices originate in the ceiling, they will image, (or sound like), they're coming from above the video display. While some may tell you that the brain will correct for this, and "interpret" the sound as coming from the visual image, that has never been the case for me. I always hear the speakers as point sources, connected to, or disconnected from, the on-screen images.
Combine the above issues, and that is *not* a recipe for good sound.
If you must have "built-in" speakers, consider in-wall speakers mounted in the front wall, around the video display. This is your best chance for audio/video lockup and for your listening position to be in the proper dispersion pattern of the speakers.
At that point, your only real concern is to ensure your speakers are well insulated from the walls they're installed in. Selecting only speakers with their own integral enclosures will ensure this:http://www.cepro.com/article/how_to_...er_systems/D1/
Good luck building your system.