Q:
Users are unsure about purchasing Traktor Scratch Pro software to use with the XONE:4D as it appears you might also need to purchase an Audio10, Audio8, or Audio4 DJ Interface as part of the package.

A:
The XONE:4D is a fully Traktor Scratch Certified hardware device and we can confirm that using turntables, or CDJs, for playing encoded 'Scratch Control' vinyl or CDs does not require the addition of an additional interface.

Users wishing to run Native Instrument's Traktor Scratch Pro software, with a Xone:4D can purchase the  Traktor Pro 3 software package:
https://www.native-instruments.com/en/products/traktor/dj-software/traktor-pro-3/

This is the full Scratch enabled application (without Native Instruments' hardware) for use with Scratch Certified controllers.
If you own or are thinking of purchasing the Allen & Heath XONE:4D, you do not also need to purchase an Audio 10, Audio 8, Audio4, or other external interfaces.