It works fine with Yosemite and El Capitan (note that Avid has discontinued the old Euphonix MC Mix). Avid has not yet approved it with Sierra, but they will.
There is one small problem though:
But that has more to do with Steinberg than the operating system.
When you’ve bought the AVID Artist Mix, you need to create an account on the Avid site. You will then be able to download the latest driver. The latest version being 3.4. The Cubase side of things is installed when you install Cubase.
Keep an eye on this, macOS 10.12 (Sierra) support information for Media Composer, Pro Tools, Sibelius, EUCON, ISIS and Avid NEXIS , for information about Sierra compatibility.