The biggest difference is in the preamplifier. The tube sound is darker, and the transistor sound has a higher micro dynamic density. So Spectral sound is more vivid. You can refer to this article to analyze your equipment.
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?