I've never had an STX, but I do have a Mixamp and DSS which use DH mode 2 (you can't adjust it).
Honestly, I would make sure you don't have your computer set to monitor or playback sounds (aka play them "twice"), or not to sound weird but make sure you aren't hearing sounds from your computer speakers the same time as your headphones. I've had my TV playing the same time as my headphones a few times (slightly delayed), and it took me a while to realize two things were playing the audio. Your comment about hearing your own mic audio is what makes me suspect this, like you're hearing the game and you're hearing a second copy of output after adding in the mic to the mix.
In the video, he says the flash drive has to be formatted to FAT32 format type, your other flash sticks might need to be erased and reformatted.
I will try again Evshrug..first I thought t had to be 32gb,,but it's just called flash 32!