Here's my response coppied from the gear page list just to start things off
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I run my Mark IV at Full Power, Class A, Pentode with 5881 power tubes. Lead Channel set to harmonics. In the loop I have a Peavey Valverb and a Chandler Stereo Digital Echo. I use those mostly with R1, my clean sound which is the channel I use most of the time. Since I use clean the most I set up the amp for what I think is best there and then try to dial everything else in. Pick which channel you think you'll use the most and go from there. I think I get a nice shimmery clean out of it, but know that these settings (especially the power settings) will affect the other channels as well. Experiment and Have Fun!
These settings are close to how I set up R1 for clean and with the other settings I'm trying to get close to what you asked for. [Rhy 1: A nice full, shimmery clean; Rhy 2: A bold, cutting rhythm crunch (ala James Hetfield); Lead: A warm smooth lead tone (ala Slash)]
I put the Master Volume at around 3. More than 2 really brings out the voice of the amp. Under that are still some good sounds but the settings all seem more extreme to me.
R1 Gain 7-8 Bright In
R2 Gain 9 Pull Fat
R1 Treb 6-8
R1+R2 Bass 3
R1+R2 Mid 5
R2 Treb 6+
R1 Pres 6 (I don't pull shift on the presence for any of these)
R2 Pres 5
Lead Pres 5
(Next Row)
Lead Gain 7-9 Pull Fat
Lead Treb 4
Lead Bass 3
Lead Mid 5
Lead Drive 6-8 Bright In
R1 Master 3
R2 Master 3
Lead Master 4-5
Try the EQ in a classic V (that's in the manual) on R2. It might bring out the crunch some. Sometimes I just set up the EQ to give me a little boost for leads on R1.
Also play around with the R1+R2 bass, especially while you are in R2. It adds crunch, but can add some mud to the R1.
Also play around with the overall Master Volume with these settings. Between 1-2 on my amp is a huge difference, between 2-4 another jump and then from 3 or 4 on up gets a little louder with more subtle tonal differences to me.
I tried to set-up the settings in this post so it will be easy to copy and paste and add other settings here. Anyone else up for a try, or have some other favorite settings?