The 950 doesn't support using a microphone to do calibration. A $30 SPL meter from Radio Shack will let you do a very good job getting levels calibrated, however, and even with automated systems such as is beginning to be offered I would tend to still double-check with a meter.

When comparing a new 950 at $700 to a used Ref20 (for example) that is four years old and costs a bit more, consider a couple of things: does the other unit offer the 950's features (triple adjustable crossovers, component video switching, Pro Logic II, analog bass management on 5.1 input, stereo bypass for analog inputs), and does the warranty make a difference? A new 950 will come with a five year warranty, while a used unit may only have a year or so worth of warranty left (or less).