AppleTV, iMac, and APX problems

I just set up my AppleTV and I have a quick question. Before I got the AppleTV I had two APXs and my iMac to stream music throughout my house. Now that I have the AppleTV I took one of the APXs out. Is it possible to link my iMac, AppleTV, and APX together? It seems like whenever I try to link all three together I am getting an error message within itunes.

Any help? Thanks.

After playing around with the settings within itunes. I got all three to communicate with each other. The problem I am having now though is if I have all three playing (imac, APX and AppleTV), I can't control the music from the AppleTV remote. Should I be able to control the music from the appleTV remote or only from the iMac?

thanks.