I believe the sound difference is because you can think of the Headsix/XXS as a mini 2Move. Think of the Headsix/XXS as a 2Move missing not just only the DAC, but also the ability to switch inbetween High and Low current by jumpers. The 2Moves extra oompf in sound is from it being able to run in High current mode. The Headsix and XXS are both in Low current mode. This was mentioned somewhere in the Headsix sales thread.