I tried my LS50 with an old Denon AVR vs my Halo A22/Cambridge audio preamp and found little audible difference if any. What makes a lot of difference is using it with a good subwoofer. I suggest you keep the Onkyo, save the money for high quality audio source (CD, SACD, digital PCM, DSD files etc.). Once you reach the LS50 and a good quality receiver or integrated amp and subwoofer(s), the quality of the audio source becomes most important if you are after sound quality. "Upgrading" to a lower power NAD is not going to do much for you.