I've still got to get used to it, but ended up last night with the gain on about 4 and the master on about 6 (not that there are any numbers to go by). This was on a hollow stage that ate a fair bit of the power and our rock covers trio about as loud as we get, so I'm fairly confident it should meet my needs for most places we play.
As I said I'm still getting to grips with it. As far as I can tell so far it's like it has valve emulation all the time, so the gain has an effect on the tone. It's nice though. I'll have a further play with that at our next gig on Friday. The 'manual' doesn't say anything about that apart from to keep the gain low to keep it clean. It mentions it affecting distortion when vintage or overdrive is engaged.