I'm trying to find the best way to set up my home audio in a 2 storey house.

This is the current set-up.

An AirPort Extreme
A iMac

Downstairs living area
A large screen monitor and set-box (which I use as my TV ( My laptop also plugs into this for movies and shows).

I'm trying to find the best solution (hopefully for under $500) that I can connect to my downstairs TV setup but will also allow me to play music from my iMac / laptop / iPhone.

Ideally it would be portable ( or have portable speakers ) so I can listen to music outside or upstairs.

I hope this all makes sense and would appreciate any advice.

So far the best I can find is the iHome AirPlay but would prefer something a little more robust.