I have one coming from Harold @ http://stores.ebay.com/Super-ATVs he is a board sponsor. I did not know he carried those and it's at a good price in case it is too loud I will not be out a lot. I will do a write up on the install and try to take a video of it so you can hear how loud or at least know the sound.
I have used the Pure Polaris Muffler Kit PN 2874650 on all my sportmans 400,500,700,800. Its a slip on maid for Polaris by Wihte Bothers Raceing. You can get them at ridenow.com for 159$. A bit louder and will give some tork.
I put one on my 700 Sportsman with a 800 hearder WOW what a ride.