Seems to be a fairly
well documented issue that's plagued the ASUS ROG Xonar Phoebus since launch that STILL has yet to be
corrected with the latest driver release of 7.0.1.30.
The problem is that when using a 5.1 setup and a new audio stream starts (say you run a game, or play a youtube video or open up an MP3), seemingly at random there will be an audible 'click' from the speakers. After that the 5.1 setup becomes all screwed up. The rear right speaker will cease to function, the rear left speaker will produce audio from the front left speaker etc.
The only work around is to close the current audio stream (i.e. close your game/audio player/web browser), switch to another speaker profile and then back again to 5.1.
It's pretty ridiculous that this bug still exists. Will we ever see a driver release that corrects this issue, because honestly I'm losing faith.