This is great! Thank you so much for the information. I will start the process tomorrow.
You are welcome.
I know this is a little bit off topic, but I post it here because it could also help another head-fi fellow, even most of them experienced audiophiles.
Your room modes (the bass response of the room in different locations of it) depend mostly on your room dimensions, meaning that your main speakers placement wont affect much, but your listening position will. Before setting your subs, you can use the Sound Analyzer app to find the listening position with the smoothest bass response with only your main speakers playing. Then try with different speakers separation and toe in for the best tone and soundstage and just then follow Jim's steps for the subs.
It takes time, but its totally worthwile. The more time you spend on it, the best. Im a little bit lazy and did all in two afternoons.