I am still working on it on the Mark V but, on an original Mark I, I would use the input 1 with the famous 7-2 setting (at home).
Volume1= 7; Volume2= 7; Master= 2; Treble= 7; Bass= 2 Middle= 7; EQ off.
No Gain Boost, no Pull Bright, Presence= 4, Reverb= 3.
Open back 1x12 cab with an Altec 417-8H, also 350 ms of delay
I've read also here that two other members agree on the following setting:
V1 = 8
V2 = 8
master = 2
T = 7-8
b = 2-3
m = 7
presence = 3-4
Regards