Does an analogue mixer with USB interface send a signal for each channel or just the main mix signal to the receiving medium (i.e. external hard drive, laptop, etc.?)
I think it depends on the Desk you're using. Without any information about that, nobody will be able to help you. Please just give us more information.
Unless otherwise specified, a mixer with a USB interface will only stream the stereo mains to the connected PC, and one stereo signal from PC to mixer. There are mixers doing 16 or more channels both directions, but that would be a feature mentioned in big letters in ads, on the package, on the homepage etc.
