well, I can tell you what I'm planning on using next...
First, I'm using double weight mass-loaded vinyl as a first layer after doubled birch ply. Then using 1" thick graded wool felt. Ive tried most of the stuff that is marketed for this application, so I figured it's time to try something else, and see what's out there for use in industrial applications, and this is what I decided to try out.
Unless you're willing to build the same design over and over, it's very hard to compare building techniques. I have a acquatance who is doing this with the above technique and should have some accelerometer data in a month or so to compare.
Another idea is to look at the E.A.R. products and put them between the layers of birch ply in a constrained damping type configuration.
In general, I'd say the North Creek building guides have some very unique and effective techniques that you could look at. Also, I think there's a book by Bollock (sp?) on the subject as well, but I've never bothered to track it down.