XP64 isn't supported but Cubase runs on it. I run LE, LE4, SX3 and C4 on Media Center with no issues aside from the known ones. This is not a Media Center issue.

It records and plays back fine, it's just triggering in real time that's the problem.

Vista has Media Center built in.

If you aren't going to try it then there's no sense in continuing this way.

What specific problems can be attributed to Media Center in your experience? I'd really like to know.