Twc,
My dedicated sound room has what you mention as floating walls. I used 5/8 drywall for the inside walls, screws spaced every four inches and used a sound blocking product to help elimate my music from leaking into the house between the two walls. I do not recommend putting a sub floor in over your concrete unless you are more into Home Theater than 2-channel audio or are using speakers that do not reproduce deep bass. If your current listening room has an elevated floor, you will notice a much tighter base in a room with concrete floors with much less bloom in your low end. I'd also recommend adding one more dedicated circuit for your lights in the room. Put in dimming light to add ambiance. It makes a ton of difference when you get into some serious listening. With an extra circuit, you will to pick up any noise from that dimmer switch.
My dedicated sound room has what you mention as floating walls. I used 5/8 drywall for the inside walls, screws spaced every four inches and used a sound blocking product to help elimate my music from leaking into the house between the two walls. I do not recommend putting a sub floor in over your concrete unless you are more into Home Theater than 2-channel audio or are using speakers that do not reproduce deep bass. If your current listening room has an elevated floor, you will notice a much tighter base in a room with concrete floors with much less bloom in your low end. I'd also recommend adding one more dedicated circuit for your lights in the room. Put in dimming light to add ambiance. It makes a ton of difference when you get into some serious listening. With an extra circuit, you will to pick up any noise from that dimmer switch.