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!
For the preamp, RCA Blackplates (NOS) provide a very open smooth soundstage; not too expensive.
I'm guessing these are the 12AU7 tubes and the phono stage is the pair of 12AX7 (ECC83).

Telefunken are more detailed, Mullard NOS have a classic tube sound, but very expensive. For a new tube, EH Gold Pins (Electro-Harmonix) are very popular.

Some good info on tube types at Brent Jessee

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.