Personally I think it's a bad idea to run the MV dimed. You open up things to way too many problems. Tubes aren't what they used to be. Tube quality today sucks. NOS tubes are way too expensive, and honestly they're only a little more reliable. Tubes were not designed to be played in massive distortion, especially power tubes -- the military didn't want tubes to distort. Remember their original use.
Guitar players found that if you turn up the level the tube starts to clip. Hence the sound of rock. Hence the legendary Marshall Plexi and the Fender Bassman. And the smaller EL84 amps. When power tubes clip the sound is good for most people, but the volume is real high, and risk to the tube and amp become greater. And because these amps were so loud they started making things like attenuators, the Marshall Power Brick being the most famous, to control volume on a dimed out amp. Still the volume just gets softer but the risk remains high. This is especially true if the bias is off. Hence the arrival of the Master Volume knob.
MV amps are designed to provide the clipping in the preamp rather than the power amp. Some people prefer a combination of the two types. Modern metal people seem to like preamp only because it is tighter.
So what I was told, and found out the hard way, was that power tube distortion = bad = danger to the amp. I had a Marshall JVM. I actually liked the amp and the tones I could get with it, but I was doing the MV dimed like everyone else and regulating with the preamp and an attenuator, and my power board fried. See they used to use lead based solder. Now they use tin based solder. Tin based solder require special techniques, and under high voltage tin can form "whiskers" and arcing on a circuit board. Your Randall amp and every other amp out there that has RoHS on the back has tin solder. Lead based solder didn't do this at least not to the extent that lead free solder does.
Just a warning. It may sound good, but can you afford it? I'm in a situation that if this amp fries like that it if it is not under warranty it becomes a door stop and I use a POD through the powered monitor that I use for my keyboard.
