First of all: I am sorry for the very late reply.
Thanks for the info lano1106.
Until now i did not file a bug at alsa but found a working solution for my system's problem.
To make it short:
did the trick.
default-fragment-size-msec = 125
I do not know if i missed this when reading the previous search results but i just accidently found it when doing a new search.
So i think pulseaudio is to blame.
Two weeks ago i also tested alsa successfully using the and directly adressing it to my hdmi out.
My systems current configuration: gentoo-kernel-3.14, pulseaudio 5.0, ati-drivers-14.3_beta