Main thing is the SXR weighs a ton, and for freestyle you want to get as light as possible. You should be able to get the 750 to easily put out more power than the 800 (stock). Then get some footholds and start playing around. Footholds aren't needed for basic stuff, though help with the more aerial specific tricks (and I prefer having holds even if I'm just rec riding). My perspective is rolls are more rider and technique than power, so just need to ride your ski balls to the wall and once you are able to manipulate the ski however you want on the water (spin it, carve, slide, etc. all the things that require good balance), then can try throwing it around in the air.
That's my general path I'm taking to try and roll/flip my 650sx. Always try to be squeezing more power out of it one part at a time, and in the meantime just try pushing myself further and further and perfecting what I have until I'm confident in my ski and my abilities to throw the thing around off a wake. Keep in mind rolls hurt if you mess them up usually (broke off my primer from my knee hitting it trying a roll), so all the more reason to not get ahead of yourself. My $0.02