I had done some research on this a couple of years back considering the same thing. It's noisier than I like in the salon and I'd like to correct that. But, like many improvements, it's been placed on the back burner. My thought was to apply the barrier on TOP of the floor and below the carpet pad to make the installation easier. Besides, I didn't think I'd need more soundproofing under the cabinets and settee.
Here's the stuff I looked at.
http://www.soundown.com/index_Marine.htm
The folks at Sounddown sent me samples to consider. I don't recall if any of their material would be suitable for this type of installation.