LOL, knew I opened up a can-o-worms.
There are of course several ways to do this.....
Using RCA cables, they make filters that attach right to the end of the cable, then go into the amp.
They also make ones that go on the speakers these would go in series with the speaker cable, through the XO, then out to the speakers.
For both options you would need 2 pieces of each. Both are about the same price, with their own pro/con
Yes, you would want a hi-pass filter for the mains, and a low-pass for the subs. Sorry for the confusion
here is some info so you can better understand....
https://gr-research.com/hi-pass-filters/