@hiend2 "Going to bring in a set of speakers and amps and listen to someting fimilair, the room the system is in now are almost the same dimensions, will report" there you go. Listen and see what you have.
Since you will still be using the space as your garage and/or shop you may consider putting some drywall at selected locations on the walls to help reduce the amount of absorption in the space. Less about isolation and more about room acoustics and reducing the amount of absorption. I would normally suggests just using plywood on the walls in a space like that so you could use it to hang shop/garage items but sheetgood products like plywood and particleboard are still very high cost relative to last year. Drywall is more expensive as well but nothing like plywood. If you have a shop I'm guessing your relatively handy and you can hang the drywall yourself. Don't need to finish it if looks aren't a concern but this will help reduce absorption in the space. Best of luck!