Tube preamp for pass labs ?

While not running a Pass anywhere your wattage, I have a Linear Tube Audio microZOTL level 2 with my XA25. It’s a great combination to my ears. The LTA is not as warm sounding as some other tube preamps, but is dynamic, great soundstage, and very natural sounding overall. The class A Pass has a bit of warmth to it (besides thermal), so they mate very well in my system.

I found after many tried. CAT SL1 mk3 Line Stage with upgraded caps & wiring. Still sounds as good as any, that’s why it’s still around and a winner! Pass needs a great tube preamp to hear its resolve. 

The next positive surprise and very musical with inner details are Allnic preamps  musical & smooth.  

Check out Aric Audio online. If interested follow up with a call. Great 6SN7 line stages. Tube rectified, point to point wired. Aric is great to deal with. 

I use one of his preamps with my Pass XA-25. 

Does "finally broken in" imply you weren't happy with it at first?

There's a Rogue Audio 99 that was used with a Pass Labs XA 25 on Ebay for $1400 right now. You might ask the seller what he experienced with it.