after some of your suggestions I made the following test:
in UI2: I open KDE Desktop, and playback a file there. Sound is choppy and breaking off. Now if I click on "stop media station" in the lmce control pannel, the sound becomes perfect when the media station (meaning all the LMCE components running on that machine) is stopped! Start it again, and the sound becomes choppy again.
I then tried to kill various devices while Media Station is up, such as OrbiterGL, App_Server, HAL etc, but that didn't bring back sound so far, so I don't know yet which particular device causes this.
One thing that could be important and that I didn't mention so far: I have a development environement setup on this machine, as explained in the wiki. Is there maybe any possibility that installing this dev environement updated the one or other library, and that this could be causing the problem? Somehow there must be a difference between my system and your guys' systems, so that could be it? I think that the problem was already there before I installed the dev environement last time, but I'm not 100% sure.
And as a reminder, sound is always Ok in UI1.