ath_gr your initial post is nearly two years old and you probably have a new laptop anyway. Maybe this will help others, though:
I have an AH531 connected via HDMI to an external Iiyama XB3070WQS (30"), on a 2560x1600 resolution.
My current OS is Linux Mint 18.3. There are no additional drivers necessary that I am aware of, the only slightly tricky thing is the configuration via RandR.