100 hz at the top end or the low end of the filter. you should be able to get a lot lower than that.

 

100Hz is a fine crossover point, whatever you think sounds best.

glad you figured out the ANC, that was going to be my first recommendation. The ANC screws with any additional equipment.

make sure you get some high pass filters on the speakers in the car. that will make a huge difference in volume and clarity.