that was John Petrucci's touring rig. he switched to the Mesa Road King amp heads, I see.
to make your tone heavier, back off the gain and play with the EQ a bit. I don't use pedals like the Boss Metal Zone and mainly rely on my amp gains but the same applies; play with the gain, presence, treble, mid and bass knobs to get the best tone that cuts through. my amp gain is usually around 10:00 or 11:00, presence at 11:00, treble at 12:00, bass at 12:00 and mid at 9:00 or something. some people scoop out all the mids but i have some in there to give my sound a bit more overtones when I play; this works pretty well for pretty much all my amps except the Diezel - i use even less gain on that amp than I do on my mesa boogie amps.
try playing around with the pedal and guitar combinations as well as string guages to focus in on a heavy BUT non-muddy sound.
the octave will not help; an octaver is not used to make a heavier gain sound.