Thanks for the hint but I don't really think this has the same source for my problem as I didn't have de-synch of audio until now and stuttering is not occationally appearing. And it also appears in Windows Media Player.
Do you have a guess for another player to try the playback?
I don't want to give on that right now - but - if it is the integrated HD 3200 (+ maybe the HT) it should be solved with your card as it has its own memory, isn't it?
Did you set the memory of the GPU to 512 MB in the BIOS?
Yes. 512MB.
Also, already tried to increase GPU frequency to 700 MHz - no effect.
Is it save to increase/overclock the HT frequency (separate entry in my BIOS) to 1200 MHz?