suggestions for hanging inner "cathedral" ceiling?

I am building a room-within-a-room and my (very reasonable) drywall contractor who is hanging 2 layers of 5/8" (with GreenGlue between each layer) on my exterior wall can build the interior wall/ceiling but only works with steel framing. We were thinking of using 16 gauge steel for studs and joists (hanging 2 more layers of 5/8" with GreenGlue between layers). Rod's book mentions steel framing and indicates light gage (25 ga) is good for sound isolation but is limited by the amount of dead weight it can carry but I want to be able to hang a ductless HVAC unit and other non-structural items on steel wall so am leaning to the heavier gauge (16-20). Should I go with steel or use 2x4 wood framing? Any suggestions for using an isolation hanger between the LVL ridge beam and the interior steel ridge beam? Mason INd. has the HD & WHD DOUBLE DEFLECTION NEOPRENE HANGERS but attaching to the LVL is not obvious to me. I want to maintain the "cathedral" openess of the space. The interior dimensions are approx. 27' x 18' by 13.5' at height of interior ridge. Thanks for a wonderful resource.

If you're using the really heavy gauge steel for structural support of the dead load, you can use RC1 to hang the drywall on, or use the RISC clips with hat channel to isolate it from the framing.

Thanks Aaron. I can see the use of RISC or GreenGlue for hanging the drywall. My question is how to isolate/attach the inner room ridge beam to the outer room ridge beam and maintain the overall cathedral ceiling openness without needing trusses or other structural material. I cannot directly attach joist hangers between the existing outer room ridge beam (see photo in 1st post) and the new inner wall studs/top plate because my HVAC ducting will extend below the existing ridge beam by about 4 inches.