As the NAD M50 has only digital outputs, the most important thing to measure is the quality of those outputs. Using my top-of-the-line Audio Precision SYS2722 system (see the January 2008 "As We See It" and www.ap.com), I connected the M50's AES/EBU output, which I'd used for all of my listening, to one of its AES/EBU inputs using a 45' length of Apogee 110 ohm balanced cable.
The SYS2722's input impedance was set to 110 ohms; the NAD's AES/EBU output impedance was close to this at 125 ohms. Playing 24-bit files, all 24 bits were active in the M50's…