I have a mix of EH and Ruby tubes in my studio and quad, seems to work very well
I've been meaning to call up Bendinelli and see if he can do anything with the studio and quad to make them closer to C+ specs. Since it's always said that the studio and quad ch1 are spot on IIC preamps, I would think he could work a little mojo on them
I recall someone from the HC forums having a "IIC+" mod done to a Studio pre. From memory, they did a comparison of their IIC+ and the modded Studio, running direct through some kind of cab sim, and it sounded pretty sweet.
I liked JJs in my Mark III. Sounded nice 'n' thick and warm, no harsh highs. Once I get my Quad fixed, I'll be trying out JJs in that too.