One of our customers had a NAD 2200 that had been upgraded submitted to the well respected Audioscience review web site. (www.audiosciencereview.com). The review is very complimentary, and I am pleased that an independent review confirms my own experience with these units.
A couple of further details are worth explaining. When NAD built the 2600 and 2700, both of which use much of the same circuitry as the 2200, they made certain improvements in both quality (e.g. Film and Silver Mica for ceramic caps) and power rail decoupling (additional capacitance), and these have been incorporated in the NAD 2200 upgrades.
Additionally there are some modern components that were simply not available, such as the Schottky diodes and audio IC’s, which have also been incorporated into the NAD 2200.
Please read the full review at:
https://www.audiosciencereview.com/forum/index.php?threads/nad-2200-vintage-amplifier-review.13960/