If you cannot find the stereo mix option on your new XPS, or Precision laptop, you should check if your computer came with SoundWire installed. The latest models of Dell computer are moving away from Stereo Mix and changing to the Realtek SoundWire HW Audio Codec Device driver.
SoundWire is a new Audio Interface Specification. It consolidates many of the key attributes in mobile and computer audio interfaces. It provides a comprehensive interface with scalable architecture. It can be used to enable audio features and functions in many types of devices. It supports the use of advanced amplifiers and microphones. In also optimizes speaker protection, microphone power and performance, noise cancellation and always-listening audio input.
Open Device Manager:
Press the Windows + R keys together to open a Run window. Type devmgmt.msc and then click OK.
Open the Start Menu, type Device Manager and open the application from the list that appears.
Right-click the Start Menu and select Device Manager from the menu that appears.
Go to Sound, video and game controllers and expand the category.
Can you find the Realtek SoundWire HW Audio Codec Device Driver in that list?
If you cannot find the SoundWire driver, it does not look like SoundWire is installed.
If you can find the SoundWire driver, then SoundWire is installed on this computer.
The computer is working as designed if it comes to you with SoundWire installed. This is the latest version of Audio driver available.