Try to set output bit depth = 16bit, and dither = on.
That does remove the problem but introduces a few new ones.
It makes it impossible to play 24 bit dts files, and playing 24 bit files by converting them to 16 is kind of blasphemous...
It looks like your DAC mutes quiet signals.
What output plugin do you use? Since you wrote "when played through any of the other players at hand there is no problem" -- maybe DirectSound plugin can solve this issue?
Considering no one else has had such issues, it's more likely that it was your drivers/your hardware than fb2k's output component.
and only when using the WASAPI component.