I've been using the mk4 mode on pentode for that chuggier kind of tone.. (i thought extreme was just too scooped and bassy sounding) pentode just sounds more modern i guess.. what i found out was that pickups and guitar really do contribute and may have a bit to do with that tone as well. my tone used to be supper thin, annoying, trebbly and scratchy, I swapped pickups and there you go.. (bkp blackdog 7 in a 7string mahog body/wenge top, bolt on hard maple neck/ indian rosewood FB)
I've been using the head with a 4X12 stiletto/trad cab (helps getting a fuller tone really better than a small 2X12 cab)
For a chuggy tone I'd go with the treble knob on 2 o'clock and the gain around noonish maybe a little more - with more treble but less gain, you'll keep a fast attack, but less compression in the sound and it's not so tight but gets looser by a little margin.. I do not overdo it with presence neither, i keep it around 10 o clock maybe 11.. if i set it higher, the upper mid character gets more apparent..
i do not recommend scooping 750Hz by pushing these to the bottom line, it really depends on the cab you use, but you definitelly do not want to get lost in a band context, a certain amount of these 750Hz mids keeps the sound 'full', mine might be in between the middle line and the bottom line.
