Another vote for changing out your cables ~ w/o spending a fortune, you could go w/Synergistic Research Foundation cabling ~ I was a bit amazed when I installed them in my system...it would be a significant upgrade, and give you at least a good chunk of that detail that you're chasing. And I agree w/everyone else who said that the PASS Labs amp is almost certainly not your problem.Don't be an unbeliever when it comes to cables, they really do make a difference; if you have bad/cheaper cables, and you dive into the deep [but not deepest, unless your main driver is a Ferrari, or your wife is OK w/a second mortgage] end of the pool, I'm guessing it will be your last upgrade.
Recommendation for a highly resolving amp
I have Don Sachs 2 tube preamp driving Pass Labs X350.5 driving Sound Lab M545 ESL speakers. I like the sound very much, but when I went to hear my friend’s Spectral system (driving Quad2912 ESL) I realized my system can benefit from having a higher resolution amp. Spectral amps need all Spectral preamp/cabling, which would be quite expensive. What would you recommend?