The MTS works like this:
* your modules have a gain + tone stack + channel master (pre-FX loop)
* you have Density + Presence + Master Volume
* the master volume is Pre-phase Inverter
This configuration allows you to open up the amp master and regulate your volume using a combination of channel gain and channel master volume.
You do not need a Hot Plate or other attenuator with this amp.
The master volume is not like any kind of variac or attenuator.
I run my master at noon - 1:00 and my channel volumes at around 10:00. That's loud enough for the studio. For a gig I'd open up the master more and work with the channel volume.
Turning the channel masters too high can cause clipping in the FX loop. Go only as high as needed.