I've used the staggered stud walls a couple of times and they're very effective and I agree with the others here, that metal studs would be horrible (just swing a solid core door into a metal stud wall "firmly, don't slam" and watch it flex 1/2 inch or more).A couple more ideas to think about:
1. Dedicated circuits for the equipment (try to wire to the top of the main electrical panel).
2. Use an exterior fiberglass door (insulated with weatherstrips) and stain/paint (get door with wood graining).
3. Suspend the ceiling down from the floor structure above to isolate. (Drywall can be hung from gauge metal furring strips that run opposite the structural members.)
4. Use flexible, lined, fiberglass insulated ductwork (cheap) to minimize furnace noise.
We're completing a new house with 8 ft x 13 ft x 21 ft listening room that incorporates most of the above (builder didn't want to suspend the ceiling). The additional cost for the above is minimal (wiring $20, door $50, ceiling $150, flex duct $0 for me as that's what he wanted to use anyway as it saves most of his labor).