B_Rich: I have one I use as a USB DAC (because honestly it sounds better than my RME Babyface Pro). However, I run mine off of a powered USB hub. Were you running yours off a hub or directly plugged into the PC? Have only had this for a short while....hopefully the USB implementation is not a cause for concern. On a separate note....I bought a 2.5mm TRRS cable for my HE4xx and am only getting sound out of the left ear when plugged into the ES100. I am thinking (hoping) this is a cable issue and not an issue with the unit. Unfortunately I don't have additional 2.5mm cables to test...nor additional amps that have that connector.