hmmmm very good question. I was assuming that since Linuxmce is a server type system that it would be written to take advantage of the multi core CPU, also remember that it is based upon the Ubuntu Distro, so that is probably were the multi-core utilisation should be occuring.
Being new to Linux and LinuxMCE I dont know.
I will ask on the Ubuntu forums if they know more about this issue, and drop a note back in this htread when I get an answer.