So, I tried 6L6s...

[Jedro]

.....and I did not notice a huge difference in tone! I used to play 6L6s, my 50cal had 6L6s and so did my 395 power amp but have been using EL34s for awhile, actually I have JJ's E34L variation in my MV. I really expected a huge difference, mainly in the clean tone. I didn't get that real Fendery clean tone, I mean, it sounded great but it wasn't what I was expecting and wasn't far off from what I was already getting with my E34Ls.

So after a day, I swapped back..

 

[Chester]

I guess the JJ's put the response in a similar ballpark. Try some winged C EL34s and you should see a more marked difference when going to 6l6s, but perhaps not to your taste

I had problems getting my sound in CH3 with =C=s, but the amp responded better with 6l6's. A real turn up for me as I have el34s in my other amps