What makes you believe your amp is not sufficiently resolving? Speakers, placement, room and source, IMO are far more likely culprits. Pass Labs are excellent amps. And for the record, i design amps yet doubt that's where you need to put your money if you want to biggest result....
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?