Unless the builder who built your home had AV in mind you just have your garden variety volume controls (no amps built in(a-bus system) or control) that just control volume and need to be amplified by an external amp. (Was that a bit redundant?) Anyway, there should be 1 4-conductor speaker wire run from a central location to all the volume controls and 2 2-conductor speaker wires running to the speakers. If you are lucky they ran a cat5 to each of the volume controls because that really opens up your options in terms of control if you ever want it.
Its mainly going to depend on how many rooms you want to be able to listen to something different. If you just want your main zone (5.1 system) and all the other speakers to be your two zones then all you are going to need is a receiver that can process and amplify the second zone. pretty much any midrange receiver you buy new is going to have this functionality. I know most newer denon's can use digital sources for second zone, but not hdmi audio feeds. I'm not sure what model this starts with but the CI (custom integration, denon's more feature filled models) is a safe bet. Otherwise you just need to run analog audio along with your digital audio sources that you want in the second zone, as was mentioned before. Yamaha is also a good route to go for second zone being implemented fairly early in the model line up You are also going to want a speaker selector to balance the ohm load the receiver sees. Please don't just wire nut together all the speaker feeds and connect it to the second zone amp, this will fail unless the impedance can be set at the volume controls(can be a pita).
Cliffs
-You most likely do not have amps built in at the volume control locations (this is a much more expensive solution)
-Anything (almost) newer will be able do second zone and internally amplify it (usually instead of amplifying surround back channels in 7.1 system)
-anything above second zone will require additional amps
-get a speaker selector (selects pairs of speakers on and off, makes 8ohm load on receiver)
-Congrats on the house purchase