"Pooh Bear" wrote
in message

I'm interested in passing stereo audio over USB in both directions.

One means for doing this is the network device model. There are a number of
devices that implement a peer network between two computers over a USB
interface. You can move just about any kind of data there is over a peer
network.

Shift gears to Firewire, and Windows has the required driver built in.

I believe that Windows already has a 16bit driver for this but I want
24bit.

There are a goodly number of 24 bit audio devices that run on USB. AFAIK
they all have to provide their own driver.