You can, for example, use two or more software audio generators/synthesizers/sequencers to produce audio streams sending them to VAC Out, and record the mixed stream from VAC In using any recording software - Windows Sound Recorder, Sound Forge, WaveLab, Cool Edit, Gold Wave, Cakewalk, Cubase etc.
http://www.ntonyx.com/vac.htm
Pues eso.... un cable de conexion virtual
Saludos