The 1220 will work excellent, even at much higher crossover points. Its mainly because its frequency response is very flat (+/-1dB), so it blends in nicely (as long as its well positioned). Case in point is the many Maggie owners running them up at 150-155Hz with little problem but initial positioning. When I use my 1220 (depending on which system its in) I normally crossover around 120Hz with great result. Its even easier than my Vtf's to make disappear within the soundstage.
You should be able to use the 100hz crossover, given that you place the sub near center so that you don't start localizing it being in some off-center location. The 1220 is remarkably colorless. I've played music through various subs with the xo completely disabled. It's midrage is quite clear, sounding like a speaker with burned out tweeter. This is as opposed to other subs whose midrange sounds absolutely colored.