Unlisted screen resolution

On my new computer I have 2 screens connected on the igpu of a i7 processor, 1 using hdmi. the other using dvi. Both screens are the same but the one connected using hdmi has a wrong resolution inside X, and it can’t be selected inside the settings. How can this be solved?

Split a physical X display into two virtual displays?

I just purchased a TripleHead2Go and configured it using OSX. What this box does is simply take 1-3 multiple external monitors and combine their signal into one single resolution. I’m using two external 1920×1080 displays with it, bringing my display size to 3940×1080, alongside my laptop’s regular display of 1920×1200. My laptop is running FGLRX 8.95 with Catalyst 12.3, the video card is an AMD Radeon HD 6700M. Here’s what I’m looking at, presently: