Nice an early MkIII with the 105 PT.
Man, someone drilled a lot of holes in that front baffle.
Guessing they thought it would help with cooling though I'm not sure how much all those holes really helps when the front grille is on.
If it has the R2 mod then the direct out is acting as a volume control for Channel three (probably what that label on the back is indicating).
You can easily see if this is true by using channel three (aka Rhythm 2) and seeing if it in fact the Direct Out knob does change the volume for channel 3.
I have no idea what the LD on the back label indicates.
Who or what is "Mad Creations"? Are they the ones that did the R2 mod?