In addition to the several brands of class D amps available, we just released a new custom buffer for the NC500s. This buffer allows the use of both 8 pin dip op amps as well as 2 6 pin pro op amps. The "No Holds Barred" model comes with 2 Sparkos Pro op amps, Sparkos P & N channel discrete regulators, and choice of Elna Silmic or Nichicon Muse caps. I attached some pictures for your viewing - if you are interested in purchasing this design, please don't hesitate to reach out.