So when I type in "dxdiag" into the run menu and find my display, it only lists my intel integrated graphics. This is AFTER switching the default to my GTX 960M in the Nvidia Control Panel. How do I know if it's switching to the proper graphics card when I'm using programs like 3DS Max and ZBrush?
"Default" simply means the nVidia GPU will be used everywhere supported -- remember this is a muxless system - software controls the GPU, and ALL video data passes through the Intel GPU on its way to the display panel (the nVidia GPU has no physical connection to the LCD panel).
That means the Intel GPU will always show active.
If your application supports software-controlled hybrid video, the nVidia GPU will be used. There are applications that do not support this setup - they require a true, discrete GPU this system doesn't have.
These are high-end applications and this is not a high performance graphics system - check with the publishers of the software packages in question to see if they do support running on a system without a discrete GPU option.
On some software, that will work. Autodesk software packages such as mentioned here very often require hardware controlled hybrid video -- for that, the XPS is not suited and you'll need a different system to run the software effectively.