I am not familiar with the NDS, but very experienced with other Naim digital and I will say the power supply makes a huge difference in the sonics. If you are not using the XPS power supply, you should definitely audition it. When I upgraded my CDX2 with the XPS, the improvement was transformative. The sound was so much more harmonically complete and musically satisfying. If you are already using the XPS, it's true that the 555 is better, but maybe there are other things to be addressed first.
