ive had heaps of problems integrating a sub within my room due to a null point at my listening position at 80Hz which sucks out all the energy. I experimented with heaps of different positions, room correction and room treatments.
what worked best - I placed the sub itself at my listening position. (Had it sitting on a mdf board balanced on a bar stool), I then played a song with a tuneful bass track (you want something that is complex with a range of notes. I used a track by Kingswood called Golden has a nice running bass line which is pushed back into the mix and generally hard to follow on a poorly balanced system.
I then crawled around on all fours listening to the bass response in different parts of my room. In some spots the bass was louder but one noted in others you really felt the null point. I tried to find a spot which had the best balanced sound and allowed me to follow the bass line without any noticeable peaks or nulls.
This ended up being against my far wall about a third in from the back wall. not a conventional position but I'm now very happy with the bass integration i'm achieving.