Before purchasing the Cronus Magnum 3, I auditioned it at home with the stock K120 and didn’t like the overall sound especially with older recordings. When I returned it to the dealer, l told him I didn’t care for the sound. I tried KT120 with my previous Primaluna integrated amp and didn’t like the sound either so I installed KT77 tubes which improved the overall sound. Fortunately the dealer had a set of used KT77 and installed them in the Cronus. We were both surprised how more musical and less glaring the sound was compared to the KT120. So I ordered the Cronus with KT77s and couldn’t be happier. I also replaced the preamp tubes with NOS tubes.
There is no guarantee you will experience the same. It might be worth spending $200 for a set of 4 KT77 instead of going thru the process of trying other pieces of equipment. If you do try the KT77 you will need to reduce the bias from 35 to 30 as recommended by Rogue. Good luck.
BTW- Live at the Fillmore sounds great especially Stormy Monday