There is a way to split the output of your graphics card from within SongShow Plus over more than one display by using a Matrox Graphics Expansion Devices, commonly referred to as the DualHeadToGo and TripleHeadToGo devices and the Monitor arrangement options within the SSP Display options.
The hardware part of this is fairly straight forward since the Matrox device will do most of the work for you. With this device connected to your projection output of your video card it will still be seen as one output but will be stretched across two or three screens, depending on which device you get.
Simply connect the outputs of the Matrox device to the adjacent monitors/screens/projectors and you have a very wide display.
There is software that comes with the Matrox device but for use with SSP, the Matrox software does not need to be installed at all because we control the device internally. If you do need to install the Matrox software for some other purpose, make sure the settings are all unchecked and at default configurations to ensure it does not override the SSP control.
The splitting part within SongShow Plus has been covered in detail in the Feature Review post on Split Monitors
You can also find additional details about the Matrox products in SSP here