What to Look For in a Home Theater
Sounds like an incredible house! And how nice that you have the resources to consider buying such a place. At that price level, you should expect a very high-performance home theater.
I'd want to be sure that the ambient light can be completely controlled at any time of day, which is more likely since it's in the basement. Can the room be made pitch black? The walls, ceiling, and floor should be a dark, neutral color, preferably gray or black.
Assuming it has a projector and screen, get the make and model of both, along with the screen size and distance to the projector to make sure the screen isn't too large or small for that projector at that distancethe projector's manual should include a range of appropriate screen sizes and distances. Has the projector been professionally calibrated on this screen? How many hours are on the projector lamp? If more than 1000, you might have to replace the lamp sooner than later.
Ideally, the room has been acoustically treated by a professional, taking into consideration the sound within the room and isolation from the rest of the house. Also, what is the make and model of the speakers, and where are they located? If they're in-walls, make sure they were installed optimally for those particular models.
What preamp/processor or AV receiver is being used? Has it been set up for this particular room and speakers? Of course, you can do this yourself, but it would be nice to know that what you're hearing when you try it out is the best it can be.
Are there good sightlines from every seat? If there's more than one row, are the back rows raised so everyone can see the entire screen? What is the viewing distance? Is it appropriate for the screen size (about 1.5 times the screen width for a 16:9 screen)? If not, can the seats be moved?
How is the system controlled? Is it intuitive to use? If not, can the control system be easily replaced?
If you have an A/V question, please send it to firstname.lastname@example.org.