Tube Rolling for Rogue Audio Cronus Magnum 2

Never had that amp but did own Rogue RP-1 and RP-5 with ST-100. 
I liked gold lion in the amp in 12au7 and 12ax7.
For the preamp the best tubes I tried were Brimar CV4003 from Upscale.
I also tried rca clear top from Vintage Tube Services (Andy) and found them a bit too hot up top in the treble. 
Gold Lion proved to be good again in the preamp as well as amp.
Didn’t care for new production Mullards and Tung-Sol. 

Having owned the Cronus Magnum II, and looking to best answer your mids and highs needs, I highly recommend RCA Clear Top NOS. I have rolled many other NOS brands, but to achieve what you want, definitely try the RCA Clear Tops.

Not quite apples to apples to the CMII, but I own a Stereo 100, driven by an RP9 preamp. I’ve gone through many combos of NOS(ish) gain and driver tubes in the ST100, and have settled on CBS 7729 (uber quiet wide bandwidth 12AX7 type) as gain and 7730 (uber quiet neutral 12AU7 type) as driver. This combo is hugely dynamic, extended on both ends, and adds very little coloration of their own. Beats any European (Amperex, Mazda, Telefunken) combo I’ve tried. The Amperex med grade 12AX7 + 7316 are a close 2nd I’d say. I did not like Mullards in there, as they were too veiled, almost "phasey" sounding in treble. RCA black plates in the ST100 are excellent, but do "fatten" up the sound just a bit too much, although that is good for some music. 7729-7730 are the winners overall. I suspect the CM will respond similarly. These 7729 are worth the hunt if you can find them. Easily my favorite American 12AX7 type tube.