i would agree, my c370 is smooth sounding so perhaps a brighter sounding pair of speakers would be good. b&w 603 s3 and dynaudio 52 spring to mind. i like the sound of my MA s6's with my nad, very easy to listen too but still bags of control and insight.
From my experience: JBL, Ruark, Tannoy Saturn (dual concentric designs) and NHT work well with NAD amplification. Also NAD have a "relationship" with Dali speakers, or they used to. Because of this I would reccomend listening to them if you can find them.
KEF, Castle and Mission 75 series don't like NAD amplification. As the others have said smooth. less bright, sounding speakers tend to be a bit lifeless. More upbeat speakers are a better bet.