NHB-18NS’s while the output impedance was a high 2500 ohms at low and midrange frequencies, rising to 3080 ohms at 20kHz, the output impedance a little high for some power amplifiers.The NHB is sort of like a highly glitzed up Lightspeed Attenuator, it’s output needs to see to see an input impedance of the poweramp to be at least 33kohm or higher. The input impedance of the D’agostino Classic Stereo power amp is 100kohm, so you have a great match. Should sound very good.
BTW: looks like a powerhouse amp. http://www.roksantrading.com.hk/upload/201601/06/201601061314126789.jpg