Quite frankly, your desire to have a preamp that sounds less "muddy" than the CAP150, uses tubes, and costs less than $1000 might be one of those situations where you can "pick 2 of those 3 things".
Aside from the Quicksilver mentioned above, there are very few tube preamps that might not sound "muddy" to you relative to the Classe. A Marsh P2000t might work for you at around $600 used. (It was a steal even for its list price, IMHO.)
You might actually do better with solid state in that price range, such as a Classe DR5 or Musical Fidelity A3cr.
Better yet, though, you might be best off selling the integrated and getting a different integrated amp. Maybe a used Electrocompaniet or Plinius, for example.
That's probably what I would do with my money, as I feel it would be the best bang for the buck upgrade towards your stated goal.
Michael