I would like to help, but I honestly do not know what the issue is with out a better description. Can you tell us the model of the "7.1 USB Virtual Adapter"?
That being said, if it is just an issue of not enough bass, you could always use an equalizer to boost the low end frequencies. For best quality, I would lower everything but the lower frequencies, and raise the computer volume.
If that does not work, try looking for frequency response graphs for your USB product. If you do not think what you are hearing matches what the graphs show, try contacting the company. You may have received a faulty product.
That is all I can think of.