I don't think is what he needs
I'm just guessing here....
I friend of mine has USB speakers and, to me, the sound is pretty low....
If you said you wanna internal speakers and USB playing at the same time, is because you want more noise.
I bought a Creative 2.1 2400 Slim, 2 speakers and a subwoofer....man, it's fantastic.....I don't need the internal speakers any more, they are resting new since I bought this.
If I understand right and more sound is what you need, this is my advice.
best regards
Guigo