Is a subwoofer 'overkill?'

Sounds to me like there isn't optimal integration. When crossovers, phase & level are correctly adjusted, there should be no distinct impression of bass heaviness or low frequency accentuation, just a sense of greater acoustic space, a clearer acoustic window into the music that's fleshed out with harmonic completeness. A good start for inexpensive help is Rives Audio's calibrated test cd that's designed to work with the Radio Shack SPL meter. It really helps to use a bit of calibration dialing these things in. Level, contour, phase controls, etc. don't always have effects that meet logical expectations.

Assuming you're running a powered sub, connected with RCA's.

I'd suggest using Rothwell 10db attenuators, which will allow you adjust the pot on the sub to a much more optimal setting.

I use this method with my Sunfire sub and it allows for a MUCH smoother intergration with my main speakers.

It really makes a HUGE difference.

You may be exciting room resonances that were not evident before. If the SW does not have its own equalization circuitry try a Behringer DEQ2496. The RS meter and Rives CD will set you back about $100. For $350 or less the Behringer will do a better and much easier job of showing you what your problem is, and after that it will fix the problems, which the RS meter will not do.

Velodyne SMS-1 EQ/RTA is the way to go. You can smooth out the bass peaks/valleys and when the wife gets home, put it in night mode in which reduces output up to(user adjustable) 20%-90%!

+1 on room mode excitation. Try some different locations away from corners and walls. Set your crossover on a low setting and then bring your output level up until you can detect the sub working. Women are more sensitive to low frequency then men.