I am not sure what your budget so I can’t make a recommendation but I do not think you issue is the amplifier. Your pre-amp has a tubed output stage with 6SN7 tubes. What tubes do you have in there ? They can impact your sound significantly. You might try a Pass Labs pre-amp or other solid state linestage as well.
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?