I have the 50w Einstein... great amp, but havent heard it with anything except EL34s - even the VH4 @ my recording studio has El34s in it... so i dont know what to say about the difference...
I DO have experience swapping EL34s to 6L6s in the JTM45 i used to own. Gain became gutsier and a bit more present, where as the EL34s were definitely the old-school Marshall tone... Hendrixy drive to AC/DC crunch. 6L6s brought it to Tool 'Undertow' era tones. I'd imagine that the effect would be similar, due to the English flavor that Diezels seem to be derivative of.
I much enjoyed experimenting with different preamp tubes. I have a sweet collection of vintage/used Telefunken, RCA, Sylvania, Mullard, Tung-Sol and GE 12AX/AT/AU7s, so i've really run the gamut of preamp tweaking. I dug the toned-down, bluesier gain that was achieved with the AT7 in V1, although there was a diminished output scenario. Right now i have all Mullard 12AX7s in the preamp, with the PI being a 12AU7. Zero fizz at any volume, and when cranked, the amp is GORGEOUS sounding.
what i love about Diezels is the fact that there is no effort at dialing in a useable tone. no matter where you put a knob, the tone delivers.
As per the comment regarding 'good/bad' pedals - i dont really subscribe to that ideology... the fact that the amp sounds great makes each pedal a valuable color on your palette. The loops on the amp are brilliant. While the gain on the Einstein is worth the price of admission alone, the spectacular clean channel makes having other 'preamps' on my pedalboard very sensible. If the the other settings on Ch. 1 werent so damn juicy, i'd be completely satisfied with only being able to switch between Ch 1/2, due to how well the amp takes pedals out front.
the other two modes on Ch. 1 clean up very well though. Ch. 2 is also very versatile, but i find that although there is more gain, there is a volume difference between 1/2 - i usually have to either turn down ch 1 or turn up on 2 in order to unify levels.
Mega mode, ch 1. rules. I'd keep it on Mega forever and just clean up on my guitar, and use 2 for leads... but like i said... the other two modes are beautiful.
Diezel covers so many bases. Why get another amp??? there are starving guitarists playing thru Gorillas in India. Don't be gluttonous.