[Al Skierkiewicz]

The wall has got to go so you can start by making that wall skewed to change at least one parallel surface. You want to eliminate parallel surfaces in the control room as well. You want isolation between the two rooms and the only way to do that is to add mass and minimize coupling. A simple way is to reconstruct with the MDF double layer on one side of the wall. and then add two layers of drywall on the control room side. If you have room, I would suggest a 2x6 header and sole plate plate with 2x4 studs staggered so that the two sides of the wall don't touch. Be sure to add caulk to the 2x6 before you lay them in place to seal against the floor and ceiling. Caulk all openings and the entire perimeter of the wall on both sides. If you must have penetrations through the wall, don't place them back to back. i.e. electrical boxes, mic cables, speaker cables, etc. When you finish the penetration, be sure to caulk around the boxes so there is no opening. You can fill the space between the walls with insulation if you want but that adds very little to the isolation. I am guessing you are going to have a window in the wall. I would spend some real money here and get a true studio window and be sure to caulk all around when it is installed.
If wall thickness is not a concern, then building two standard walls separated by an inch is better. Mount the MDF on one and the drywall on the other. then you have no connection between the control room and studio. If you want additional isolation, then another sheet of drywall can be added to the inside of one of the wall. HVAC ducting should not be common to both rooms either. A little thought can fix this with a longer duct run and lined duct. The majority of noise inside a studio that is isolated from the outside world, comes through, or is generated by, the HVAC.