I modded the bios successfully and increased the mining speed to ~14.xxx mh/s with the following settings:

bios mod:

1750 timings -> 1875, 2000
max memory clock 2000 -> 2200

amd radeon settings:

gpu clock -> 1125 (underclock)
memory clock -> 2000
fan -> 100%

ASIC is 65% and 75% so they run 60° and 53°. Memory is Micron 4GB.
Could push the memory clock further now but I'm satisfied and let them work for 48h.

I think they could do 15.xxx mh/s but with much more power draw and heat dissipation.

And disable crossfire in amd tool, enabled by default!