I'm familiar with the Dynamat brand of sound deadener. It's primary purpose is to deaden sheetmetal panels and to insulate the heat from under the car, roof and firewall. Dynamat is a thinner more dense material, almost like a very thick tar paper that's a bit on the rubbery side. The stuff a friend of mine used on his streetrod also had a silver foil over the top side, which could hurt garage door openers if it were blocking the direction of the signal. This would also be counter productive for the use with backer material for speakers. It would take any rattle out of the fiberglass though. Maybe they have something new that is not foil covered.
As far as its use in a fairing compared to the foam supplied FREE with the J&M speaker kits, my opinion is that the foam will do more for us in our fairings as sound absorption material than deadening material. I think it cuts down the out of phase from the rear of the speakers and helps to get more in phase sound out the grills. It stops the sound from bouncing around inside a fiberglass enclosure.
Dr. V-Twin offered me the option to "upgrade" to the Dynamat, but I stayed with the freebie foam and I'm glad I did.
And for the sticky backer, I was about to give up on getting the paper off to actually stick it in the fairing until I took out a razor blade and cut in the middle of one of the paper peel patches and found out how to peel off the paper. It sounds simple to just peel that paper off, but once you get the hang of doing it, it is a lot easier.
I am really impressed with the J&M 7.25" upgrade speakers. (For the money...) I'm sure that Hawg Wired and Hog Tunes have great products too, but without an extra amp, the $219.95 delivered to your door is not bad.
I had a kick butt system in my Willys streetrod with two amps, Bazooka sub, Infinity speakers and Eclipse head units. It was awesome to say the least, but there were issues with it while driving. My exhaust was 3" all the way and with a blown 392" hemi it made lots of noise. On certain tracks and certain artists, the low frequencies of the exhaust would cancel out my low frequencies of the speakers and it was painfully just some mids and high frequencies getting through to the ears. Now when I was at a show, it was the bomb.
I'm thinking that in our world, bikes with lots of low frequencies from our mufflers (or lack of them), any sound system we install and try to listen to while driving is going to be taxed to the limit to not get cancelled out by our low frequency exhaust.
Just something to ponder...