I don't recall ever seeing anyone comparing the SQ of HDX vs. Core, with or without NDAC.
But there have been lots of comparisons of Unitiserve and Core and most say that using the Naim- supplied SMPS power supply for the US, the Core has the edge on SQ. I would say that opinion in the Forum is about equally divided on whether the Core sounds better via upnp or s/pdif, but anyway it's generally thought respectable either way.
So this isn't answering your question but maybe it will help get a discussion going and flush out someone who has compared HDX and Core into NDAC.
best
David
