First try to find the cause of the problem. Then you will be in a better position to know the best way, and place, to fix it.

Sounds like it could be a ground loop.

1. unplug all cables from the Modx - use headphones - is there still a buzz/noise?

2. repeat #1 using monitors connected with UNbalanced cables - still a problem

3. try plugging the Modx into a totally different power source that isn't shared with your computer - run a long extension cable if necessary. Ground loops are often caused by sharing a power connection with the noise maker

4. Confirm you are using a USB 2 cable and not USB 3 or other. It CAN make a difference although others not always.

5. While the buzz/noise is being produced try moving the USB cable around and see if that affects the buzz/noise level or dynamics

6. Try rerouting the USB cable so it isn't near, and doesn't cross any other cables.

I'd try the DI box before the others unless one of the others is available without spending any money. 

Well ...

Ground loops are caused by equipment using different outlets with ground at different potential values and the suggestion would often be to either plug everything into the same outlet (mixer, Mac, keyboard, etc) or use a ground lift to cheat.

Here's a reasonably non technical article ...

https://www.prosoundweb.com/troubleshooting-hum-awe/

Alternatively, noisy aggressors bleeding into the audio path would be something like running unbalanced cables parallel to some noisy lines or over some relatively high powered high frequency stuff which would pull for balanced if that's going on which DI's give you as long as you're running a short (less chance of noise) unbalanced line to it.  This wouldn't be an example of ground loops.