First off, kudos 's for putting some air behind Couch Two....
Sub crawl method works with any single sub, as you only sit in one place. Adding a second unit poses a logical problem, but one that's been addressed, at least partially by Geddes and Harman. This link discusses both, with links to each method.
http://blog.acousticfrontiers.com/whats-new/2010/10/29/using-multiple-subwoofers-to-improve-bass-the-welti-devantie.html
Of course, if ears are the only measurement gear, Geddes method won't work, but his advice of 1 in corner, 1 mid-wall is sound from the perspective of energizing the full range of room modes. Conversely, the body of work from Harman says middle of opposite walls are the optimum place if using 2 subs in an ideal room...
The unique aspect is what your specific room needs, and what you can do so it's livable as well as sounding good. There are lots of variables, but a few things are fixed, like wall locations and resulting room modes. See what you can get, then let us know what you still don't like. I'm betting on at least one strong room mode... let us know what you find out!
Have fun,
Frank
