The disgusting out of date drivers to be honest and lack of support from ASUS. Alot of games had sound issues and such. It seemed dolby headphone sometimes would cause artifacts in the game sounds. I confirmed this by turning it off and on. The sound panel is so clunky and rediculous and the drivers had really high DPC latency so sound would pop a lot.
A lot of problems were alleviated by installing 3rd party "unified" drivers but not all of them were gone.
Music was fantastic though and thats where it would shine. Really prestine sound quality from the DAC and headamp. But I game a lot too and couldnt justify the STX just for music.
In the end I bought the Z and all the problems were solved, in fact their HRTF seems much cleaner and higher quality than dolby headphone. The ZXR was my goal but ill suck up slight loss in audio quality until it comes out.