I'm very certain the Benchmark AHB2 is the most resolving amp available... but you'll need to bridge mono them to get the same power you're getting from your Pass Labs.
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?