It seems you want the clean sounds to be louder and the distorted to be about where you have them, (volume wise)? In the first posting it seemed like you just wanted to lower the distorted sounds to be equal the clean.
Lowering the plate voltages will not lower the gain enough to be noticable. The lower plate voltage will result in a stage with less headroom and more distortion.
If you want less gain in the clean, you can switch in paralell resistors in the plate so as to lower the plate load and thus the gain. To keep the cathode current at the same levels you could at the same time switch in a series resistor in the cathode which will lower gain even more. But I dont think this is what you want?
It seems to me your amp is at it's limits and if you crank the clean any more up it will start to distort? In that case the only way to get the clean and the crunch to be at equal volumes is to lower the crunch. That means you use your amp for monitoring, and mic it up for all the rest to hear. Unfortunately that is the norm these days. It seems clubs are taking more and more control of the sound. Most bands are limited in how much they are allowed to turn up their amps, and instead everyone is mic'ed and a sound dude sits in the back with all the controls. Understandable that the clubs want the best sound for their customers, but it also ruins some bands since they often sound better when they are in control of their own sound.