Wow, that's a surprising input on the compatibility issue. I'll have to check in with my friend as he's never mentioned that issue to me and I know he has Khorns (as well as Belles and LaScalas). Glad you were able to get some input from the good folks there. The gain on your pre is significantly higher than mine (mine is 18db unbalanced, and 24db balanced on my work system going into the Mini-Mites pushing Heresy's which are only 94db efficient). I'm not sure what the gain is at home with my Cary SLP-50A. The only noise issue I have is with my Sonic Frontiers SFP-1 phono stage which has a 37db output in the MM stage which I'm using. With that I have identical tube noise issues to what you describe with all kinds of tube combinations. This is going through the Mini-Mites which have the 18db higher gain then the Horn-Mono's (in my work system). I'll let you know if I hear back from my friend to see if he has similar issues. Thanks for posting your findings as it is useful information to me with my Sonic Frontiers issue!
Marco
Marco