first i disabled EDID in xorg.conf then i added the file i /etc/ati/amdpcsdb
EnableRandr12=SFALSE
EnableRandr13=SFALSE
and entered the correct values for VertRefesh horizsync and refresh
well now Xstarts with 2048x1563 :-) and it still ignores my modelines.
but now iam able to change the res and refresh with the catalyst tool to the values i need.