Speaking for the result of a 2nd sub.. I had no other choice than to go in opposite corner with the rear next to my LP. What I've seen is evened out response in my room. In diagrams I've seen, placing a single sub in a corner shows the best response in the corners of the room. While having two hasn't resulted in a greater overall amount of bass, it has evened out the response. Where I used to get maybe 40% of the response in the dead center of the room with my single, I now get maybe 80% to 85%, which I'm pretty pleased with.
Btw, I'm already really enjoying the speaker choice for music. Pretty soon here all switch over to movies, so I'm looking forward to that as well. Niw I just feel like I need to get bipole surrounds