LPF / HPF help I am confused

I have a new sony cdx-m850mp head unit with built in  filters, it has 3 sets of preouts (1 for sub), i am running an polk ex12 sub and four gxr polk audio speakers, what do i set my head unit filters on, there are two settings

first one is "LPF" 85hz or 125hz which should i set it and the other is "HPF" again 85hz or 125hz are the only two choices?

I notice a small differnce when i change them and personally i do not mind either setting i just want to be sure i am treating my speakers properly so I can get longer life/use out of them

thanks

-kirk

the highs are coming from the head unit right now. i am looking for an MTX 404 but i can't find a resonable price $170 range. anyhow now they are straight from the deck and the sub is out of an mtx 202.

as far as i can tell the deck unit is either "hard wired" to the outputs or the sub is "preset?" ie. when i get intot he head unit menu the choice comes up ...LPF...85hz or 'click...125hz THE the next choice is HPF etc. it never says that one is for sub output or speakers outputs?

The nice thing about having the settings built in to the head unit is that you can constantly adjust them depending on what type of music you're listening to or what type of sound you want.

Just make sure you use either the head unit's crossovers or the amp's crossovers, and not both at the same time.  So you'll just leave your amp's built-in crossover (if it has one) to full range output.