I don't think that the MBA supports multiple external displays. Only 1 through the Thunderbolt port with a VGA or DVI converter.
There are three solutions:
- Thunderbolt daisychaining with two Apple screens
- Matrox Dualhead2Go DP edition with two non-Apple displayport screens
(Matrox software maximizes applications to one or both screens)
- Thunderbolt plus Additional USB 3.0->DVI/DP adapter (not available yet but announced) to two non-Apple screens
I use the Matrox Dualhead2go and this works flawlessly