There is no way anyone can suggest you the best position. Get a loooong RCA cable and do the sub crawl. Nothing else works.
Regarding configuration, in your receiver you'd need to do it manually. Make sure all speakers are set to small, crossover for all speakers set to 80/90/100 Hz(try each one, pick what sounds most balanced), set crossover on sub to the largest number on the dial. Now play a track with clean bass, have a friend sit with your sub holding the volume knob and you sitting at primary listening position. Ask the friend to increase the volume on the sub till you just start hearing the bass. That's your perfect volume for sub. You can increase or decrease a few notches based on preference. This works great if you have done your sub crawl correctly and placed the sub in the best position possible keeping aesthetics in mind.
MaSh