the linked article provides a lot of generic note detection info, and i don’t believe anyone said no audio interface would be required.
whether or not the nu’s are superior to gk2/3, graphtech, rmc etc. is an open question.
in my personal experience piezo’s have proved to be both reliable and effective, plus they’re easier to maintain/install than the gk’s or the nu’s.
this is a video of my mg2hex setup in action:
using this system, a notable plus is that a long held chord on piano fades out naturally. this is not possible with boss synths like the gp-10 and sy-1000, with them holding a piano chord till it fades out produces weird artifacts and highly unnatural cut offs.