Your call.
Yes - it's going to absorb some bass, the question is where and how much. It's totally dependent on exactly how you construct everything else and as was stated earlier, it's WAY too easy to short out. Don't take my word for it. Ask respected room desingers like Terry Montlick and Dennis Erskine. Neither of them recommend using RC in any audio related room.
As for the space, yes, it takes a little. But, not nearly as much as a separate wall structure and the extra space is part of what makes it more effective by dropping the resonant frequency of the cavity.
Lastly, the RSIC system will also provide some absorbtion in the bottom end. Now, if you want a poor mans way to replicate a % of this performance, you can just use slatting perpendicular to the stud faces and mount the drywall to that. I'd recommend this over the RC. At least I know in advance what it's going to do.
Good luck.
Bryan