I don't know if the Linux USB drivers support this, though.

The Linux USB support does allow USB speakers to be plugged in and used. How to reverse this to the laptop, I'm not sure.

With the power requirements, I believe the empeg needs 1A max, due to the drive spinup. The biggest problem I see is trying to connect the power from USB over to the empeg's power circuitry.

The other issue on a laptop is that most don't provide the maximum power to the bus unless the laptop is plugged into AC.

This is all probably possible, but not worth the work.