The streaming board is the same, the Stream Unlimited NP800 manufactured for Naim
That board does all the network stuff, before sending the resulting digital data to the DAC. It’s the DAC implementation that is different between ND5 XS2, NDX2 and NSC222. By DAC implementation I mean everything from the streaming board IO through the DAC used, to the DIN/RCA plugs in the back of the unit. And even then the context within which the NP800 sits is different, as I think there are “upstream” changes between the above too, relating to streaming board isolation, but I cannot recall well enough what they are to find related posts/threads