Listening Room Upgrade

I am having the carpeting replaced in my listening room and am looking for any ideas on how to improve the acoustic properties of the room while I am at it. The only ideas I have come up with are to put down 1/4" plywood flooring to stiffen the floor and to use non-synthetic carpet. Any help with material choices and installation methods is greatly appreciated. My current floor consists of modern floor trusses(18" O.C.) with 3/4" tongue and groove flooring. I do not think I can use a material greater than 1/4" for the sub-floor because of matching considerations with an adjoining room. God bless.