Hi TU,
If you're creating the signals, why not using an analog output (winsound)?
Another point! I'm not sure if you can set different sampling frequencies for right and left channle! At list you cannot do that when using winsound. So, you have to chose a single sampling frequency.
I personally prefer this, as I feel more control over triggering.
Take a look at the attached file plz. Pass the data as, a matrix of two columns, to this function and you'll be able to hear it.
Hope that solves your problem.