Here is a "no epert" comment.
Have you tried to capture straight to a file on your main drive, say in My music.
Do you then see a wave file, roughly the size you would expect?
If you play a commercial CD in your CD player, using Microsoft Media player, does it sound OK?
If it does, so will the file you captured. I suspect there is some problem in your setup, make surew nothing is "muted" or volume turned down to zero...
Maje sure that in GS the DSP Station Output master slide is up.