If you are sure about which impedance terminals sound the best you can try some very inexpensive new stock JJ tubes in the 12AU7 spots.
The JJs come stock on the Cronus Magnum and are a dark sounding tube but still capable of great sound. This will be an inexpensive way to see if you are headed in the right direction. You can get JJs 10 bucks each.
The JJs come stock on the Cronus Magnum and are a dark sounding tube but still capable of great sound. This will be an inexpensive way to see if you are headed in the right direction. You can get JJs 10 bucks each.