Dual Subwoofer Question

[DIGITALBATH]

Premise-I live in an apartment. If it is possible, to pick up the same version subwoofer for a very small sum, should I do it? I have read that if you have a 7.1 receiver, you can run a RCA Y-splitter and have both subs plugged into one subwoofer in(out?). Sub(mine) Velodyne-V-1012-b the other in question is a V-1012X-b, but they are both the same VA series, I think that essentially they're the same, same woofer size, just a few years apart. Receiver is Onkyo TX-SR605.

So if I run the Audyssey EQ what will it do to the DB levels provided both are set to the same level. How much louder will it be? Right now I watch movies at volume 55, and can get away with 60, but I did get a little irritation from up above, so 55 is safe. What about room placement? What are some options people choose? I know of the standard L and R, what about 1 behind the couch. I appreciate the input, though I think it's foolish to consider, there is an aspect of a security blanket, just the idea of having two .