It will definitely be ideal for you to be able to "Play genre x" in specific rooms, as well as playing movies.
If you are happy now with the Shoutcast command and it is working on all machines, then great.
However, I am wondering whether the problem you are having with the radio add-on stream could be, again, a small typographical error in your VC code for sending the commands to the correct xbmc device?
If you decide you would like to try again to get that radio.de code working properly, feel free to post your complete radio add-on code for VoxCommando (including how you are sending the information to different machines), and we can try to help you solve the streaming problem.
This information could be helpful to other users who have multiple XBMC machines as well.