You should take a look at the AMD Radeon HD 5870 Eyefinity 6-edition graphics card. This allows you to simultaneously display data on six displays and allows you to set several parameters in the driver relative to the output location (3 lines, 2x3 horizontal / vertical), etc.) .
As for the API: with such a card (but also with TripleHead2Go) you get one virtual canvas that supports full 3D acceleration without loss of performance (much better than with an extended desktop). At AMD they call this the Single Large Surface (probably equivalent to what NVidia calls the horizontal / vertical range). The caveat here is that all outputs should have the same resolution, frame rate, and color depth. Such a surface may have a resolution of 5760 x 3240 or higher, depending on the settings, so it’s good that 5870 is so fast.
Then, in your application, you transfer this large virtual canvas (using OpenGL, Direct3D, or in some other way), and you are done ... Besides what you did not say if you are going to display the angle to each other or in a flat configuration. In the latter case, you can simply use one perspective camera and visualize the entire buffer buffer. But if you have more settings for "surround sound", you need to have several cameras in your scene, they all look from one point.
The fastest loop for this rendering is probably the following:
for all all objects set textures and shader and renderstate for all viewports render object to viewport
but not
for all viewports for all objects set textures and shader and renderstate render object to viewport
since switching objects cause the GPU to lose much more useful information from its state and caches than switching viewports.
You can contact AMD to check if you can add two of these cards (power permission) to one system to display up to 12 displays.
Please note that not all configurations are supported (for example, 5x1 is not, as I read from the FAQ).
A lot of my experience in this was collected during the creation of the Future Flight Experience project, which uses three beams (each with its own camera in a 3D scene), a dual Nvidia GTX 280 in SLI and Matrox TripleHead2Go in Windows XP.