Nice move. I had assumed that was what you would be doing all along. I have my double MRK series racks doing the same thing. I don't know if you thought about how your are finishing around the rack, but I offer this tip so you (and everyone else) can learn from my mistake:
Make your rough framing 1 3/4" wider than the width of the rack on the sides, 7/8" taller on the top, and space the inner edge of the rough framing at least 4 inches from the corner of any wall, if possible. This will allow you to attach 3/4" solid (or PVC) moulding stock around the perimeter of the rough framing and give you an attachment point for your 3.5" casing around the perimeter of the rack to finish the look.
The other option I used in my last house was to build a small framed box roughly the footprint of the rack, topped with 3/4" plywood. Height would be above your baseboard about 1" at a minimum. The rough framing opening allowed approximately 1/8" all around. I then used drywall "j" channel to achieve a finished edge. I pushed the rack through the wall until it was slightly proud of the drywall and finished with black caulking around the perimeter for an ultra-tight custom look. With a 44u rack the overall height does get a bit tall, but I put my whole-house amps, matrix switchers and other stuff that doesn't require loading media at the top of the rack to bring other sources to eye level and within reach.
Just some food for thought as you consider your finish work around the rack, although I am sure you have already!
You are definitely in the home stretch - can't wait to see the rest!