This is a dissatisfier for me also. Been going on hour+ rides, & my ears are ringing when I get back. I tried to add the skirt, but the polaris pump tunnel has obstructions making this impractical. I put a rubber 'flap' on the EXH outlet, but I think it is limiting power more than noise.
My immediate plan is to use earplugs.
Long term, I would love to find a 4 stroke engine, I think it would be easier to muffle without losing power. Been using 4 gallons of gas per hour, btw, would like to reduce that too.
So far I have run up on a gravel shoal, hit a rock & a log, - no damage to the boat!
It's a blast . . .