My recommendation is generally to trust the SPL meter (keeping in mind that most SPL meters are a bit inaccurate at low frequencies - there's an adjustment factor chart for Radio Shack's meter in SV Sound's subwoofer setup FAQ) to calibrate the system, but to not be afraid to adjust slightly after that to achieve the sound that you like. Personally, I run my sub at the calibration setting, but plenty of people run a few dB "hot" to get a bit more punch from the low end. Bottom line: your ear knows best what you need.