You may want to post this to a Data Acquisition forum, as you would probably be talking with engineers that have more experience with this sort of thing. However, I do have a bit of experience with it. If you are wanting to send out analog signals to the different speakers independently, you will need to have two different channels to write to. Does your sound card supply this capability? I assume that if a card allows stereo sound, it would have multiple channels to write to. Let us know what you find out.
J.R. Allen