Rogue Cronus Magnum 1 tubes

I recently upgraded to a Pass Labs XP-12 preamp and XP-17 Phono pre. I am using my Cronus Magnum 1 as an amp in this setup. It’s done by using the variable output on the CM. It runs like a bypass as there is no volume control, etc. that works on the CM in this mode and on a side note, my system is much quieter which was one of my objectives. 

My questions are, if I am only using my CM as a power amp, do I need to have the 12AX7 and 12AU7 tubes installed? Are these tubes even being used with my current usage? If I do not need them, are there caps or covers you could recommend? I am using KT120 Northern Electric tubes, would you recommend another type instead for my current setup?

thanks