You are right as rain the Mesa mark V has phenomenal distortion.
Put one before and 3 after then!
I would need one before.. for pitch shifters at minimum.
I run a pre/post rig… because obviously I need my crunch (CB Brothers) before delays or verbs.. but I need the H9 to pitchshift or wah before my distortion, no?
Maybe you dont use that stuff on the H9.. but if you have 4 of them….. you certainly CAN.
SO- At least one before the amp. At least 2 in the loop.