The following link is for a thin mat designed to improve STC ratings the cost is about $1 / sq. ft.

http://www.db-3sam.com/Pages/Acoustics.html

their report shows that steel stud walls have better ratings than wood, I think this furthers my theory that the 1-1/2" steel furring /air space helps with sound transmission

in speaking to the mfg. rep at the SEBC show, he stated "the fewer fastening points , the better STC ratings"

Would this go between the furring strips and the drywall? They've got a pic on the website in a bathroom - looks like it's applied under the tile?

I was offering this as a solution for the OSB ...STC rating, so could be directly to the panel