I'm no expert here, but I own a Rad Shack analog meter and the Sound & Vision Calibration disc, and have calibrated my system numerous times. The Dolby Reference level is just that - a reference. Dolby Reference level is usually too loud for sustained listening. I calibrated my system at 75 db, then turned it down to what's comfortable for me. I honestly don't think it matters whether 55 or 65 or 75db is used, so long as the speakers are calibrated the same.

The nice thing about the S&V calibration disc is that they use the exact same SPL meter, and give a thorough video tutorial on how to use it and calibrate your system. The trickiest part is calibrating the sub - much harder to do than the main speakers. And if you haven't done a video calibration on your TV, I'd highly recommend doing so. I honestly believe calibrating my system is one of the two best tweaks that I have done to mine (with the other being matching speakers up front - mains + center).

JD