Airport Express Airplay set up nightmare!

Wlll this looked so simple, but I've spent hours of frustration trying to get this to work.

I have a new Airport Express 811.n and I want to be able to play my itunes through my stereo, wirelessly. That's all!

I have Airport Utility 5, so I've tried this

http://support.apple.com/kb/HT1731?viewlocale=en_US&locale=en_US

No good. Ive followed John's excellent tips here

https://discussions.apple.com/thread/3929691

and tried this

https://discussions.apple.com/thread/4153687?start=0&tstart=0

but still I have major issues:

I can get everything working perfectly with an ethernet cable attached, but when I disconnect the cable I lose connection to the AX. Enable airplay is ticked in Airport Utility and I've checked the firewalls in security.

At the moment I can go online (yay!) and there is a green light even without the ethernet cable attached! Double yay! But itunes can't see the AX. If I plug in the ethernet it does.

Obviously I'm doing something wrong, but I've reset this thing dozens of times and started over. My IP address on the AX was 169.254.2.47..?

I'm not using an Airport Extreme, it's a Netgear router.

Please help, I'm going crazy!