UPDATE: Thank you, again, for all the great perspective. This really has been helpful. I managed to get a good deal on a used PrimaLuna Evo 300, with stock tubes and a bonus set of KT150s. I hooked it up with the Eversolo A6 and out to my vintage Heresys...
Wow. My first impression is that I didn’t realize my Heresys could sound so good at this age, without any capacitor or crossover updates. Playing some Gladys Knight, and Temptations the distinct, but subtle, "golden glow" emerges. My wife even commented.
Comparing several tracks side by side with my SS setup (see earlier comment), my wife and grown sons preferred the tubes! To be fair, things might be different with more dynamic classic rock and modern music. But the $800 streamer/dac into $3100 (used) EVO 300, out to $1200 (used) Heresys more than holds its own against an almost $20K SS setup.
I look forward to getting to know my new tubes better!
https://www.audiogon.com/systems/11958#&gid=1&pid=1