Maybe, just maybe your excellent amp needs a tune up. The .8 series is 8 or 9 years old, the .5's obviously older. Nelson is as good as they get. I would still have my 250.5 if I had room.
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?