If you wired a CAT-5 to each 'volume control' location then you are going to go up several price brackets because your system was designed to use 'smart' keypads, and not traditional volume controls. A typical generic volume control has the speaker wiring run right through the volume control itself so you can adjust volume at the volume control. A smart keypad allows you to adjust volume, pick different sources, and turn a specific room/location on and off right from the keypad.
This price difference is generally a couple thousand dollars for the preamp/amplifier and smart keypads. It almost always allows all zones to be run independently from each other.
So, something like this:
SERIES2&recordID=ZR-4 Multizone Kit&categoryID=Multizone Products&catcdID=2&prdcdID=FG01610
Price for that unit seems to be around $1,800 for that unit alone.
It handles discrete amplification, includes keypads, includes pre-amplifier, and source selection capabilities, but that unit alone eats up most of your budget. Niles, Speakercraft, and Sonance all make some type of distributed audio system which is similar I believe and you should look for a deal/special from any of them.
Anyway, you would really separate everything and treat it like 3 individual setups... Your media room (surround), your living room (surround), and your distributed audio system (4 zones). The keypads would go in the wall and give you local source selection and volume control, the univeral remote it comes with can be used to pass commands onto devices (track up/down/etc.) as needed. Throw an AppleTV or similar in there and you can get control from your pocket of your distributed music if you want.
The tough part for me is that I don't use that type of system, but I am familiar with them. I can't offer you deep thoughts on your options, but you have quite a few and I would consider most of your options fairly similar. The Niles solution I listed I like because it seems to be plug-and-play.
Plug in a keypad (let's call it zone 2), then plug the other end of the cat-5 into zone-2 on the Niles main box, then plug your speakers from zone 2 into the amplified output on the Niles main box, and plug all your sources into the Niles main box, and plug it in. Your keypad should work immediately. Pretty straightforward for the audio newbie.