Mark looking at your last diagram the middle of the room sure looks bare without the coffee table, you may want to consider an ottoman as opposed to the coffee table. They come in various sizes and I would imagine you can find one that will be smaller than the existing coffee table but will still tend to your needs, i.e. ... feet!
Whenever I was considering 2 subs I was told by both the Axiom and Hsu folks that catty corner placement would probably be ideal while keeping in mind to correctly set the phase for each sub. Like Wid says, maybe one in the corner by your right hand 60 and the other in the corner where you have the existing JBL sub placed in the first two diagrams.
