Ingemar Johansson has introduced a new "PRO" version of LspCAD.  

Along with the great capabilities of the Standard version, the PRO version includes capability to use your Windows full-duplex soundcard to preview the sound of your crossover network after design -- one channel per crossover driver output.  A stereo 2-way crossover is possible using a true 4-channel soundcard (with 4 distinct actual WAV channels).  This allows you to actually audition the crossover's performance, quickly, before assembly of the crossover components -- the crossover's response is computer simulated, so your computer becomes a highly sophisticated electronic crossover, capable of emulating the characteristics of passive crossover designs.

note: The latest information and files for LspCAD and LspCAD PRO can be found at