I don't have a DR per se, but I have a Road King which is pretty similar, so maybe I can help. I'm not even really sure what channels the DR has. I'd assume a clean, crunch and super-gain channel? My RK has 4 channels so I'm not sure.
Anyway, in terms of damaging your amp...if you run your master output level at unity gain (50%, 12o'clock, half-way, whatever you wanna call it) you should be able to get your channel volumes all the way up without damaging anything except maybe your speakers if they can't handle it. Of course, if you do this you'll probably go deaf before anything on your amp breaks, so I wouldn't try it. These amps are designed to be run at what I would consider to be unnecessary volumes for long periods of time. As long as you have proper ventilation for them and they don't overheat, and your speakers can handle the volumes, then you should be able to run it at almost 100% with no problems. Keep in mind, if you actually do run this amp in the 85-90% range for long periods of time, the tubes will be shot way quicker than normal, and the overall life of the amp will probably be shortened, but I wouldn't say that anything would be irreversibly damaged.
But yeah... I'm betting you will reach the threshold of pain long before you top out this amp, so don't worry, crank it up man.