I tried Nuforce 9.02's with my Quad 63 USA's just prior to selling the Quads. It was not a good match in my system either. Made the Quads almost dull and lifeless...I have used various tube amps with the Quads.from low watt El-34 and 845 SET to 60W Kt-88 amps..all with excellent results..the best amp I used on my Quads was an older Threshold S/200..just a perfect synergy of balance, warmth, and transparency with enough power to grip the panels. I also used an older Class A Bedini BA-801 that worked great too.
Im not sure if Class D amps are the problem. Another AgoN memeber who runs Quad 989's runs a pair of Channel Island Audio D-200 monoblocks and they seem to do just fine..Maybe its the Nuforce amps in particular..dont know. But they did not work well on my Quads.
I have them on my Emerald Physics speakers now with exceptional sound.
Im not sure if Class D amps are the problem. Another AgoN memeber who runs Quad 989's runs a pair of Channel Island Audio D-200 monoblocks and they seem to do just fine..Maybe its the Nuforce amps in particular..dont know. But they did not work well on my Quads.
I have them on my Emerald Physics speakers now with exceptional sound.