@OP, I previously owned a Sim Moon P5/W5. I kept preamp for over ten years, but changed the power amp more quickly as it had more of the slightly dry sterile sound you mention.
As regards Pass, you need to give them a bit of time to adjust to their presentation when coming from a more "transistory" sound. The amps have accurate pace and rhythm and present detail accurately when compared to live music.
You get what you pay for in terms of quality - the more expensive models are better. It is worth listening to the XP-27 preamp in particular and it would be interesting for you to try one with your existing power amp as a starting point.
It you want a half way house between Sim Moon and Pass - have a listen to Gryphon.