I've primarily been using a Mesa 2:90 into guitar cabs (2x12 EVM12L) and mostly high gain type tones. With every firmware update I reset everything. System reset, new patches, etc. The first thing I do after that is audition the first 40+ patches running through my KRK8 monitors. I know these aren't top of the line monitors, but they don't suck and I'm used to them and know what to expect.
My V6 experience thus far:
1. Stock presets through the KRK's are better than ever. So much so I sat and really enjoyed playing through quite a few patches tweaking very little and just basic drive, TMB, MV controls. Even the higher gain patches were so much smoother and 3D sounding to me.
2. Load one of my presets (sag control off so just preamp of USA Lead 2), reset the amp block and switch to the 2:90 and cabs. Tweaking, tweaking... Not so much fun. Very dull and lifeless compared to what it was.
3. Back to the KRK's. Spent a little time tweaking a few presets and was liking it so well I thought this may actually finally convert me to being an FRFR guy
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4. Trip to GC to pickup an EV ELX112P. Beautiful clean tones for sure, not so much with mid to high gain stuff. Stuffy, boxey tones. After some testing and running some music through the EV it just seems to lack the midrange punch for quality gain tones. Kind of "DJ-ish" sounding. I might fiddle with it more but I'll probably return it and try a K12 which I read somewhere has more mids to it.
Overall it seems the high end harshness some are describing may actually be due to the tamed down high-mid (2-3k) frequencies I found that came with 5.07, making the higher frequencies more prevelant.