I use a black marker on the outer edge of redbook cd's. It helps absorb reflections during playback. Not as exciting as Subaru's set-up, but seems to help resolution.
Best tweak
Sometimes the simpleist tweaks are the best ! The best one I've tried lately is to use some rubber door stops to tilt the center speaker down from the top of the monitor towards thr listeners' head. What are some others that have worked for you ?