Alright, after a lot of frustrated searching, I found that I had to restart my DAC. So... problem solved.
Pretty much as described. I get sound that E-APO modifies out of my monitor, but the DAC plays nothing when activated. Far as I know, Realtek doesn't "attach" to USB right? I'm at a total loss of where to start looking. I disabled Realtek because I never use it anyways, and I've unchecked both "Use original APO" in configurator.