I've done the upgrade. And I've tested it with my favourite preset with Cornford 50. First impression - boy this doesn't sound any better at all, too much middle frequencies. After some playing around and tweaking, the overall result wasn't that satisfying.
Today I have reset the amp block. Just a few knobs here and there and it sounded already in the ballpark but not tight enough. The next move I did was to switch the bright knob on, turned the cap. a little bit down, so that it wasn't too harsh but enough to shine through. This also solved somehow all the the low end at the same time. And there it was, a quick click on the "save" knob, then I played a long session. Punchy, organic, roarrr, sizzle...it's all there. Then I've reset the Brit 800 #34 and again, so simple, was rockin' in two minutes.
This is a great update. It's probably worth of reseting the amps cause it's more simple to dial in a good tone only with basic knobs.