Hi Don
Back in the early 90's I traded in my 40 wpc Technics integrated amplifier for a 20 wpc Rotel integraged amplifier. And gained a sig. imporvment in sound quality. I am sure this was because of the better preamp stage in the Rotel. I believe the Rotel, or in your case NAD, uses much better components in the preamp to improve the sound. NAD and Rotel also tend to be more basic on functionality, less bling, have better engineering to keep the singal path as short as possbile. There may also be better power supply in your NAD than you Yamaha. Add all of these together and you get a better sound.
paul
