i have an 850 an have been looking at this issue very hard. with the 550 you have many options. kolpin, stealth, (maybe same)benz, and hushpower. i have looked at them all which they do not offer anyhting for the 850. Look at hushpower. it is made by flowmaster and they have a video of a rzr and all you hear is the tires. I do think that any of these options will work for you.
2010 850 xp Stealth Black, 2500# polaris winch, Strong made rear drop rack, Atv Guru front brush gaurd with full expanded and added bar to protect bottom of rad, front lock & ride storage box, kolpin fender extension