The DR was a Douglas West A.K.A Tone Boy thing. Back in the 80's Randy, Mike and Doug would pick up the phone there often. There was no web and if you wanted something or whatever the phone was the way it was done. After owning a new II, III and IV I had talked to these guys a number of times. Many of the updates on the products came from things I pointed out to them. I was the first one to get a Celestion from then after bugging them about this for years.
I had talked with Doug many times a year or so before the first DR coming out telling him if you could do a Boogie with more of a Marshall 800 English crunch voice how cool it would be. I still remember when he told me I think I have something that well make you happy.
Mike Soldano told me my Tremoverb is a cool amp ... We talked down at his shop about him putting a resonance control on it back when I picked it up in '94. To control the bass a little better.
There is a lot in common with the Soldano and the orange channel.
If you use tubes that are more like a 8 rating on the Groove Tubes it well be more like a normal bias ..... un like 4/5/6 that the normal Boogie tubes are. Or put a adjustable bias this well get rid of some of the harshness from having cool running tubes. .... or just turn up the master to get it hot enough (not the same). It is a DR and never well be real smooth. But it is sound that is huge and aggressive.
I agree the rack mounts seem to have a certain magic to them. The Tremoverb has little more load on the front end that smooths out the sound a little. Mesa told me its about the same as turning off the bright switch on most amps. The cleans and between sound are the best to my ears with this amp. The 2 channel solo head Dual / Triple can be a bit in your face at times. But this is just a matter of taste.
Changing out a few tubes in V1 can make a lot of difference of the voice with this amp. Best power tubes I found for this amp our 20 year old 6CA7. At the price of these things when mine die I well be going to KT77.
Myself I like mids up around 2 o'clock for a lot of sounds on the DR.
That web link I put up above is the best I have found for what has gone on with these amps.