with how much hertz to cut off?

Hi guys! I have an Audi 80 B4 with doorboards. In the doors are 16 Morel Pulse 6.5 built. The tweeters are on the A-pillar. I still have my 10 CO 100 Plus of audio system installed in the amature board which still run on the radio. Unfortunately they distort at higher volume. I got a bridge 45.2x. And now to my question. The bridge have plug-in modules to separate. At how much Hertz I have to separate the then on the amature board. because they because of the missing membrane surface I don’t think you can play down to 80 Hertz!