thanks for your answer.

The reason I`ve wrote my request is that in fact XBMC (and I don`t mean OSXBMC/Plex with this - I`m talking of www.xbmc.org, the "official" XBMC port) worked with a previous version of RB without any problems at all. I don`t remember which version it was, but it was not long ago (Nov.2008?), and XBMC was still listed as "XBMC" under the supported applications.

So, if you could just enable RB to recognize xbmc.app as XBMC (maybe with the same default behaviour as Plex - like stated, this worked 100%, tested with Apple Remote and PS3 Remote) like before, everything would be perfect for me.

Plex (plexapp.com) and XBMC (xbmc.org) are indeed not the same under the hood, I`ve found the official XBMC better suited for my needs, so at the moment I`m using Plex, which is better than no RB-controlled Media Center at all.

Thanks again, 
Chris