Sorry to hijack, but I've never tried the USB myself, do all laptops send audio thru the USB? Is it a noticebale improvement in the sound quality?
Using an external DA converter, like the Peavey mentioned ,will allow most any laptop output audio via a USB port.
How noticeable the improvement is will depend on how good your laptops building DA converter is. Some are decent, some are crap. If you are going to use random laptops, not your own Apple MacBook, there is piece of mind in the peavey device which works without any drivers on Mac and Windows laptops and delivers excellent quality along with balanced outputs that can be run from the stage to FOH through a snake,... It's a good, cheap tool for the kit that will guarantee consistent results and solve distance problems,