I've had mine for two months now and love it. i guess that the definition of "acceptable volume" would depend on the level of deafness and the size of room you play in.

To try to answer. Yes, Brit and Modern are louder.
No, the gain doesn't have to be at 9 o clock to get any volume at clean and crunch, it doesn't get really really loud though, the gain is important for those two channels.

The THR amps don't just model the sounds but also the ways the different amps would work. that's why the gain does one thing on one channel and something else on another. On some channels the EQ doesn't do much at all but has a huge impact on others.

I've been meaning to write and record a review but I have so little time

/Hampus