I've never tried one of those Digitech Valve FX preamps, but I think one of Nevermore guys used one on their self-titled album. And they have a pretty cool tone on there. (found the source, dunno if it's true:
http://www.ultimatemetal.com/forum/s...more-amps.html)
I'd recommend you take the 15-band EQ out of the mix though for a few days and compare your sound, with and without. I used to use a DOD 31-band EQ in my rack and after some reading, found out they typically "suck your tone". Parametric style EQs are supposedly much smoother. I don't use any EQs now, but if I did, I'd recommend parametric. What Eminence speakers are in the cab?
Edit: Oh yeah, I just realize you use a
sonic maximizer (or something equivalent). Yeah, an EQ plus that is probably going to be a no-no, but just use your ears. If you must, use one or the other (or none even). I'd bet the Behringer enhancer would be more suitable than the Crate EQ though if you must use one.