If you’re getting clean sound from the Mac already, then you probably have no need for this. The 1/4 inch headphone jack on the front is the output, as well as the two RCA plugs on the back. The interface shows up as an audio device in the System Preferences sound panel, and effectively acts as an alternative DAC.
I solved the issue by adding an extra Behringer UM2 that I had on hand. My knowledge is limited in that area, but I do know Macs can be hit or miss on the DAC quality. Setup a dedicated network with an external router, that way you have a more robust network that can handle up to 10 control devices. A couple tips, the onboard wi-fi is lousy, and you can only connect 4 devices to it. My guess is that the headphone jack’s DAC inside of the iMac was poorly designed and actually picking up radio noise, because I could actually hear faint sounds of what could be a local radio station. Yes you can mix your own monitors wirelessly with the Behringer XR18, this is the exact setup we run in my church. This was actually helpful at one of our campuses where our 2017 iMac was putting out a lot of noise when we were using a longer cable between the iMac and our PreSonus console. The guy who needs 16 channels or less isnt forced to spend more money on channels hell never use. Thats a smart marketing move by Behringer. Sometimes you can get a lower noise floor by using one of them instead of the built-in headphone jack. The Behringer X32 Rack is less money because it only has 16 channels, but expands to 32 with the S16 digital snake which is an additional 900. Yep! You’re looking for an audio interface. The Behringer X32 is all that much lighter, though it does shave off about 10 pounds (it’s 45.4 lbs), and is smaller in a couple of dimensions, most notably the vertical dimension due to the lack of angled back.