I was just at the Home Depot today looking at the sound board by Homasote. It says its a sound barrier but it only has an NRC value of .20 so I assume it would be good for blocking sound from coming in or out of your theater but not for accoustically treating your HT interior. I didnt see the specific board you mentioned in Home Depot today but I would stress that you should either call the company or check out their website to see exactly what it is ment to do. If it has a low NRC rating then it may just be intended to be a barrier and it wont condition your rooms acoustics well. I did however see a HT install out there on the web where someone used acoustic ceiling tiles screwed up on the wall to deaden the HT front wall. You can buy acoustic ceiling tiles cheap and they have NRC values of .55 and higher. Of course you have to cover the tiles with acoustically transparent fabric or hide them behind curtains etc. I am currently looking for solutions to deaden the front wall as well and considering using acoustic foam behind curtains but you gotta shop around for good prices for the foam cause it can get up there in price. It is however more effective at deadening the sound with NRC values of .80 and higher depending on the thickness. Good luck.
Gonna name my HT "Tooth and Nails" for the battle my wife is putting up against it.
Funny, I used to think my 32" tv was big. Now my 92" screen is starting to look small !!