How do you high pass your main speakers?

You can insert some Harrison Laboratory fMod hi pass filters into the line (RCA) from your pre amp to the amp(s) driving your main speakers. 

They have hi-pass cutoffs at a range of frequencies and aren't too expensive so you can get some at 30, 50, 70, 100hz.... I got the 50 and 70's when I put some subs on my system. 70 seemed to work best for me. They filter at 12db per octave so you still get some music below the cutoff level. 

That'll take stress off your main amp(s) and leave those frequencies and below to your bass array. 

@12many 

Sorry, but the reality of the situation is that the 80kh crossover point was based on my previous speakers. I will be adjusting the crossover point to perhaps 65Hz and reassessing things.

@ddrave44 

That would be great, but I have an integrated amp.

I don’t high pass... If the speakers are good enough, I trust the designers, so I want my mains to run full range as they were designed to do. I just cross the sub to come in where the mains start to roll off. Works well.

There are a number of ways.
#1Built into the receiver or preamp is one (more of a home theater feature sadly) 

#2 built into the subs (rare) 

#3 external analogue (my choice, JL audio CR-1, wilson sub controller, Bryston makes one or at least did).  
       3a, digital crossover, mini dsp etc (cheap but complicated)

#4 adding the right resister to your wire like a crossover before the speaker