Someone just asked me about the volume boost problem when engaging the 2nd channel, thought I'd post my response here:
If you are going straight into a DI then yes, some sound engineers won't like the volume boost when engaging the 2nd channel, but it's never been a problem for me. They usually have compressors/limiters at the desk end anyway which helps. If you're feeding into an amp though, the extra volume boost can just end up pushing the amp into more overdrive instead of boosting the volume; I always try to get them to take the DI from the amp or mic up the cab which so that the PA sound matches the amp sound.
It is possible to set up the knobs so that there is no volume boost but still an increase in drive though. Each tube has 2 gain stages which can both create overdrive. If you turn up the 1>2 knob, then that increases the volume going into the 1st stage of the 2nd tube, creating more overdrive. Then you can reduce the Gain2 knob to reduce the volume in the 2nd stage. Only problem is to get the really full on distortion you need Gain2 whacked up, so you can't go from very gentle dirty-clean sound to full on fuzz while keeping the volumes in check. If you treat it as a boost to just give you a slight volume push and a bit more drive during loud choruses etc it works wonderfully.