You can cheat a bit and use the Express VI Acquire Sound which lists all of the sound devices, use Windows device manager to see what devices are there, or use Get Num Devices in _SoundAcquireConfig.llb and Sound Device Info in lvsound2.llb. Both of these llbs are in vi.lib\sound2 and are what are used in the Express VI.
p.s. This board is for digital I/O devices. You might want to post additional questions to the LabView Board.