Sunil,
Cannot speak to your specific USB audio related question, but in terms of a quality laptop, vis a vis Dell XPS, I can.
I've had really good luck with Dell's XPS series of laptops.
For audio, I'm curently using an XPS tower, with a sound card for digital out. At some point I guess I should test the XPS laptop's USB out since the Audio Research DAC7's USB DAC is considered really good.
All the best with your decision.
- David.