Those with in-wall ipod dock - please help

Ok, I have a walk through coming soon and the unit that I purchased comes with in-wall ipod dock. When I wanted to try it before I bought the place, I was told that I need to buy the "receiver" separately in order to hear the sounds from the speaker (speakers are already installed in the unit). So I am thinking about buying that "receiver" for the walk-through to make sure it works. The problem is, I don't know what "receiver" to buy. Can you guys give me a recommendation for what to buy? I don't really want to spend much since this is a place I occasionally use. Thanks for your help!