If you're interested in trying preamp tubes at all, the RFT ECC83's might get you a touch closer to EVH's sound. I've read many opinions and reviews of the tube, and they all say the change is noticeable and unique.
From all I've read, here's what to expect in a nutshell:
Break up very early, slightly compressed, lessened clarity
Fairly mid forward, a bit looser on the lows, softer on the highs
All those characteristics sound like they'd get you closer to original VH tone. Many Marshall guys love the tube as well.
I ordered some I'm waiting on myself.