Thanks for the replies, my OD has a level on it and I can set the amp clean with the OD off, then balance the volume with it on. The problem with that is the pedal isn't cranking the amp any more than when it's off, so the distortion effect is just from the pedal, not the amps output valves, and it just doesn't sound as good.
If I use the OD with just a little gain but more level, it drives the amp into beautiful touch sensitive crunch, but there's quite a jump in volume when i step on it, which mucks up the mix with the band, and drives our sound guy on the desk crazy!