I've just made the move to a tubed pre and SS amp. In my case, both pieces are from the same manufacturer, Blue Circle (specifically the BC21.1 preamp and BC22 MKII amp), which helped avoid impedance mismatch. More than that though, although they are still breaking-in, they are devliering a lot of what you've described you're looking for in your system. If you have the chance to audition some tubed preamps, you should be able to find one to your liking.
Best of luck to you.
Best of luck to you.