For a similar App I have tried JW120 Wireless Headphones,
http://www.jensen.com/wireless/jw120_linx.asp

It's a Beltpack receiver so you can use earbuds, and is a 900mhz device so it is not transmitting on any commercial bands, which also I guess makes the content you are transmitting a little more private, they claim 150 foot range, but in reality it starts degrading in the next room and certainly isn't up to scratch for listening outside the house in the garden,

But for a short range the Jensen wireless kit is really cool, and sounds great, you can dock it with a lead to recharge the beltpack's batteries which last a long time, the only drawback for my application is the range,
so I have been considering boosting the power output usng one of these Motorola 344066F Linear Amplifier Modules
http://cgi.ebay.com.au/ws/eBayISAPI.dll?ViewItem&item=1941764142&rd=1

I wonder if any of you Radio Amateur's reading this thread may have any better ideas of how I could simply boost the RF Power output, is there a better way to go?

Gazz
Alice Springs
(Middle of Nowhere)