I've used champagne yeast (like EC-1118) before with good results. I wanted to try thie Cotê des Blancs to see if it would dry out just a little less. (It did... 0.998 vs 0.996 on avg with champagne yeast LOL)
As for the Chitosan and Kieselsol, not being a wine maker, I've never used the two (always associated the two with wine rather than beer). What would concern me with trying something new like that is if they are so effective that they'd counter the effects of the dry hopping I'm doing. Have you ever used the two with a dry-hopped beer?
I've always used Gelatin with good results in the past, that's why I plan to use it this time.
BTW, I noted that there was a special on unfiltered apple cider at the Ft Myer Commissary ($2.25 /gallon). I usually only do ciders a couple of times a year, but with that kind of price, I may have to adjust my plans LOL.