Dual head in the way you want it won't work on any board by any vendor available yet. You can't have to digital outputs active at the moment. So DVI and HDMI is not possible. You can use DVI and VGA simultanously or HDMI and VGA, but not DVI-HDMI. And, actually every manual I've seen says so. So does mine for my Gigabyte 780G chipset mainboard. (I checked it for you, read your manual pages 2-20,21!) NVIDIA boards don't have the functionality either. So you expect something that plainly is not (yet) available... If you bought it for that you should have informed yourself better beforehand. Everywhere I had read it clearly says that digital+VGA=dual head.
Digital dual head will only work with an additional Hybrid CrossfireX capable card for you. Not sure if that works under Linxu yet though.
I'm using this board with a 8600GTS for some months now and I never really used the on-board video before. I still bought it for future usage though, since I usually keep such hardware around for a very long time and the on-board video will be used sometime, perhaps already somewhere next year.
I got a HDMI->DVI cable some time ago and I suddenly decided to try my luck today with the on-board video. It would be a "nice to have" if both digital outputs worked, but I can live without it especially if VGA+DVI does work.
Hence my unpreparedness, since my question is answered in the main board manual. Sorry for that!