Hello mxpx1821 and welcome to the forum.
There are many receivers from the popular companies Yamaha, Onkyo, Denon, HK, Pioneer that will do sound in at least 2 zones and there are true multizone products from companies like Niles, Nuvo, Sonance. Many of the newest products from Yamaha, Onkyo, Denon, HK, Pioneer will pass analog video to the second zones and add a third zone for audio. My Onkyo even has sub outputs for the second and third zones. The one main drawback is most will only do analog signals. So this means that even after you have all that nice new HDMI equipment you will need the old analog connections hooked up for those sources to be used in the secondary zones.
True multizone/whole house audio systems will give much more flexibility for keypads, volume controls but may not offer the best solution for a theater.
Things I would look for:
1) A reciver that will do three zones. Main HT, Second zone w/video, Third zone for audio
2) IR inputs jacks. This will allow you to use a IR system like those from Niles plug directly into the receiver and not have to use a flasher.
3) If your only using 5.1 in your HT then the reciever should allow you to use the surround back speakers as your power for zone 2. (saves buying an extra amp)
That is all I can think of now. Have you looked at any recivers yet? What is your budget? I have used/owned products from Onkyo, Pioneer and Denon and all three will do what I have described with minor differences.
Cheers.
