The primary reason producers hunt for Kontakt 5.5.2 today is library compatibility. The NCKX and NICNT Transition
One of the most common reasons producers look specifically for Kontakt 5.5.2 is due to changes in how Native Instruments handles library authorization. In later versions of Kontakt 5 (and completely in Kontakt 6/7), the classic "Add Library" button inside the software was removed. Users were instead forced to route all library management through the Native Access desktop application. kontakt 5.5.2