Tube Rolling for Rogue Audio Cronus Magnum 2

CMII owner here.  First I tried new Genelex Gold Lion 12AU7's and 12AX7's in all five slots.  A little bit better, but not night and day.  So then I got an Amperex Bugle Boy 12AU7 from Andy Bowman at Vintage Tube Services, and that also is better.  But I'm now still hankering to try a vintage Mullard in the pre-amp position, as stereo5 did.

I also splurged on new Genelex Golden Lion KT-88s to see how they sounded in comparison to the KT-120s, and after a week the 120s are back in the sockets.  More impact, more bass extension, and only very very slightly less sweet.  No reason (now, I discover) to change these.

So, my experience to date: the stock JJ's are not such underachievers as they are sometimes made out to be.  But with some expensive NOS small-signal tubes you can certainly improve and tweak the sound.

It may be aging, or it may not measure well.  Do you know any of history on it?  For $10 more, Upscale sells a specially tested one for CJ and Rogue preamps.

Also, has anybody tried using a Brimar instead of a Mullard on the pre-amp socket?  I keep hearing that they're pretty good, but the Mullard seems tried and tested.

hi! any recommendation for the center 12au7 cmiii ?.
I have these options at a near supply.

preamp spot on the cm sounds best with anything amperex or made by amperex.  mske sure it has been screened for low noise.  transparent, dynamic, clean, refined and colorful.  

i had the CM ii for several years and literally tried them all.  

12AU7 matched Mullards from Andy's Tube Services here.  I been meaning to call him and maybe try something new but the Mullards been sounding good for years.

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.