Expanding on that idea, if you are running out of juice, try crossing over at a higher frequency. Depending on your sub (FR,quality, and location), crossing over at 100hz or 120hz will take a sizable amount of stress off your mains. This could allow for your system to be played louder and clearer, with more bass, and again, for free.
Audyssey tests for the -3db point, but the receiver sets the crossover/speaker size and crossover points, even if these are not optimal. Chris K. of Audyssey makes a frequent point of telling people to ignore the small/large settings, and to try a crossover around 80hz. At the worst, it was only a few minutes of time (you won't need to rerun Audyssey, just change the settings in your AVR)
Even with my STS towers, I tend to crossover at 100hz to my subs.
Augustine's Law: "The last 10% of performance generates one-third of the cost and two-thirds of the problems."
"If it works the first time, it's not high end." ~ Harry Pierson