Preamp choice: VTL 2.5, CJ 18LS, Pass Labs X2.5?

I don't know about the others, but I used a VTL 2.5 when I had a Levinson 27 & Thiels with great success.

No one can give you an answer. They are all fine preamps with no technical flaws - it is their individual flavor that differentiates them and which is best depends on the system and the ears listening to it. Just buy one, try it, determine whether you like it or not, if not, get another, and repeat. If you buy used, you can't really lose any money so try them all one by one and then not only will you know which is best for you, you will also be more informed about what range of sound is possible. Start with the one that strikes your fancy the most and enjoy.

Arthur