True thing is, you almost never get the live sound of the amps on stage to the audience, I belive that no amp can fill an arena or venue by itself (and all musicians would be deaf if the amp could handle the volume).

All amps have mic's and are amplified by the PA so the real volume of the amp is not so high.

Zack Wylde's wall of doom are just a bunch of muck up empty cabinets with 3 "live" heads and cabs, same goes to almost any guitar player that has a big bad ass wall of speakers.

So the option bout your problem would be:

1- get your rig to run trhu the venue PA (get ready for mic headache)
2- get a louder amp (so you won't have tu crank it up all the way to get the volume you need) a tube amp I've heard are pretty loud, even the small ones.
3- some people hate this but, bottom line, is a good option, nowdays a lot of amp emulators (line 6 POD, digitech, boss GT8...blah, blah, blah), most of them pretty good and have output direct to PA, so you have lots of control over your sound and you don't have to carry a big bulky amp.

I know all this options are not always at reach but to be honest, there is not much more you can do