When I went to Win8 it was a clean, fresh install of X3e along with Rapture and Dim Pro. Rapture and Dim Pro might have been from previous Sonar versions, but they are the latest.
Both run fine stand-alone and from within X3e and S-PlatC. I do have one extremely isolated problem with Dim Pro, but as long as I don't use that particular program it works great.
This is just to let you know they can run fine in a Win8.1x64 environment.