Bandwidth issues are as follows:
USB1.1 = 12MB/s per controller
USB2 = 480MB/s per controller, several motherboards have 2 USB2 controllers now.
Just for the audio data, there is other data sent across the USB line also.(timing and packet stuff??)
16 bit at 44.1KHz(44,100 samples per second), cd standard rate, is 16 x 44100 = ~0.71 MB/s for mono -- 1.42 MB/s in stereo. USB1 is plenty good for this.
24/96 is 4.6 MB/s mono so 9.2 MB/s Stereo. USB1 would be at or over its limits..
USB2 could handle over ~40 channels of 24/96 audio then..
These numbers are theoretical and I am sure there is more to the transfers than this..