I haven't been very proactive in finishing this article.  I'll finish up my findings today.

The last way and probably the most flexible way to control audio in the home would be to buy a receiver that could be controlled via the PC, one specifically suited for that sort of design.  The best solution I found were products by a company called Russound.  They offer audio amplifiers with support for multiple zones and control via PC.  The best part is that they have a well defined software application interface (API) so that if you're comfortable writing your own control routies you have nearly 100% control over the amplifier.. everything from zone selection, zone volume, muting, power on/off, etc.

Ultimately what I had planned on doing would be have a cheap PC (everyone I know has a PC sitting collecting dust in their home, or enough parts to build one) connected to a Russound amplifier (I would have chosen something like the Russound CAS44 unit ) .  I would write some custom software to control the amplifier and this software would also be a server of sorts, listening for events from remote computers.  This way you could have something like a PDA or smartphone broadcasting events like "turn volume up in zone 1" and the PC would hear that event wirelessly and then adjust the amplifier accordingly.  It would be fairly straightforward to write all the software needed to listen for network events and to control the amplifier.  The most difficult task would be to write the software for the smartphone/PDA but luckily Microsoft offers free development studios for PDAs these days and there are other free solutions like SuperWaba if you're more familliar with Java (which can be notoriously slow on portable devices.

I never did finish my project, I had a basic server working and listening to network events fine, I had it accepting and controlling 4 zones without too much trouble.  I had a set of code working for a PDA type device but sadly my PDA won't connect to my wireless network and my brother in law decided to go for the more expensive smart home solution so I had little incentive to try and finish the project.  I'm very confident with time it would have worked very well and cost very little, everything was set up perfectly where all the speaker drops were co-located in a network room so dumping a PC to play music and control the amplifier in there would have been an invisible way to manage 4 zones of music.  There would be no need for custom keypads or remotes that only worked in single rooms.