Congrats on the purchase rjxox.
Sub positioning - you should do the sub crawl to find the optimal position for the sub in your room.
X-Overs - Once you have the sub positioned where you want, you can play with the x-over to get the best blend with your sub and sound that pleases you. Some use 40Hz with M80's, some 60 Hz and others 80Hz. I think it depends on your room and preference at that point with M80's.
Sub volume - I prefer to set my sub gain knob so that I get a 0dB adjustment on my receiver for the LFE channel after calibration. This is a trial and error process but leaves you with maximum room to bump the LFE channel up or down as required without having to reach behind the sub.
As for sub effect, it should blend with your mains without drawing attention to itself, but when there's serious LFE you should KNOW that your EP500 is doing it's thang!
My EP500 is positioned behind my couch and literally shakes the couch on serious LFE scenes.