I couldn't find info on resolution steps, but tried to solve the problem via other way,
so I searched for others with same settings:
And found this (1 year old):
- Resolved an issue where 2560x1080 resolution was not available on the third DisplayPort 1.2 monitor when daisy chained.
And this is in the FAQ:
Check with your computer and display manufacturers to find out the supported resolutions for the computer and display.
Now I think: HD 4600
- mobo bios update
- monitor driver
- DisplayPort cable