For media walls, what we currently recommend is using a Windows PC with a graphics card that is able to turn multiple displays into one larger logical display. This feature is present on quite a few professional graphics cards such as the ATI FirePro cards and is called Eyefinity.
There is quite a range of FirePro cards starting from around 200 dollars. We have tested a 6 (3x2) wall setup using the W4100 card.
Once set up the OS will see all the displays as one large display and you can run ScreenCloud like normal using the Windows app.