A zone could be a DLNA Renderer so you could stick a wireless media player such as the WDTV Live (once they get its last botched firmware update corrected...) or, if you're more of an audiophile, a Cambridge Audio NP30 or a Denon DNP-F109 or similar units, in a hard-to-reach room and connect it to an amp.
I've been wrestling with the best way to get multizone audio into hard-to-reach rooms too (2-foot thick stone walls...) and I'm currently experimenting with the Marmitek Audio Anywhere 625 digital audio sender, which is a tiny, tiny (approx 3" square) audio transmitter that can be used with multiple receivers at the same time. I'm not likely to want independent music in each room at this time so I just want whole house synchronised audio - I'll just pair an additional receiver with a pair of powered speakers in each room. There's a very, very slight delay introduced - not very much at all, but enough to be able to perceive a "hall" or echoey effect if you can hear the original source and the transmitted version at the same time. So basically, you could connect a transmitter to one of the outputs from your sound card. This system can only be used once in a house though, there is no way to pair a transmitter with a receiver so you can't have two transmitters. Marmitek have another product called Surround Anywhere which is intended for surround speakers without trailing wires to the back of the froom. It accepts line level or speaker level input and at the receiver end has an built-in amplifier so it outputs speaker-level - you wouldn't need an additional amplifier there. So if you need two wireless rooms, you could implement one with a Audio Anywhere and the other with a Surround Anywhere!
Just two different ways of sending audio wirelessly! One is over an ethernet wireless network, the other is transmitting the audio itself wirelessly.