Hi Don - Most computers . . laptop or otherwise . . have a stereo headphone output or perhaps L/Right RCA output jacks somewhere. But "stereo" means just that: TWO CHANNELS. The Pianoteq software provides for up to FIVE output channels: In the Graphics User Interface, or GUI, clicking on "MicMode" option will allow you to toggle on/off the five microphones and also to click and drag them to different virtual positions around the grand piano icon.
Here is where the I/O (either Firewire or USB) comes into the picture. Your computer can only output two of the microphone channels. The external I/O (Input/Output) device can recognize the five channels . . keep them separated . . and on the back of the I/O device (module or box) there would be the five (or more) physical output jacks. Then you run those individual jacks to five physical amplifiers and speakers or to five powered speakers.
This is the beginning of recreating the huge multi-sourced sound that a piano actually generates. A piano sends out sounds from thousands . . millions . . of different point sources. Our ears are stereo and our brain processes that two channel input from our ears.. We do not often appreciate the end result but in the case of a piano or orchestra on a stage . . terms that describe what we hear would include: PRESENCE (part of the auto-location process).
So, if you have five separate channels and speakers around your piano/controller keyboard, the sound is coming from those five point sources, but our (stereo) ears and our brain will begin to recognize that PRESENCE we are (looking) for.
Five average quality speakers connected with a multi-channel I/O will do more to enhance the PRESENCE of the piano than two high quality speakers connected in a two channel set-up.
All of the above only in my humble opinion . . :-)
Lanny Davis