Tweaking my Cronus Magnum Tubes

I'm wanting to tube roll on my Cronus Magnum. I have the KT 120's and the standard small tubes that came with the Magnum.Also have the KT 90's. Should I update the KT 120's to Gold Lion 66,77 or 88's There's a quad of Gold Lion 66's on sale here at Audiogon.

W#hat are good small tubes to update and what small tube position are most important to update?

Thanks mates!
Call Rogue Audio. Chances are that Mark O'Brien will answer the phone. Speak with him or Nick. They can give you the best advice for new tubes. They have both been a tremendous help for me as I have upgraded the tubes in my Cronus (non-Magnum)integrated amp. With their thoughtful guidance and advice, I swapped out the five small tubes as follows : an RCA NOS 5814 to replace the Electro-Harmonix 12AU7 gain stage tube, a pair of GE NOS Five Star 5751 "goldpins" to replace the Sovtek 12AX7 input tubes, and a pair of GE NOS 12AU7A's to replace the Electro-Harmonix 12AU7 driver tubes. I then replaced the original Svetlana EL-34's with a wonderfully matched quad of Genelex Gold Lion KT-77's. All these upgraded tubes get along quite nicely, and the sound of music is sublime.
I bought a RCA nos 5814 for the gain stage from Brent. Nick at Rogue said the gain stage tube was the most important small tube. Should arrive tomorrow. I also biased the power tubes for the first time in awhile. 3 tubes were off by 5 to 15 points. This made a noticeable difference!
The RCA NOS 5814 is a great upgrade. Smart purchase ! I check my tube bias about once every two months...... rarely needs any adjustments. Enjoy your "upgraded" amp, and have fun listening to your music !