If you can't put you sub between your two mains, get two subs. Pretty simple Placing a subwoofer between your mains can be awkward, but it may save you a grand or more depending on the subwoofer.
Two Subs?
With McIntosh's for amplification and Martin Logan Renaissance's for speakers and a JL Audio F113 v2 for a sub, do I really need a second sub for both music and movie performance? I'm being encouraged by my hi-fi shop to get a second F113 v2, as that is what the manufacturer intends for you to do, but realllly? I'm more of a music person than a movie person.