Sticky indeed

Forgive me mlord as this post contains much of the content I sent via PM to you.

The drafters of the USB spec went to great pains to avoid the terms "Master" and "Slave" instead choosing "Host" and "Function" tho I feel the former are more technically correct terms to describe this type of system I will use the bastardised USB terminology.

Yes you are correct the USB spec says Function devices can't talk to each other.

I see four options three of witch require custom hardware and all need software changes to the Empeg.

Hack the Empeg to implement USB on the go.
" " to output something (in violation of USB 1.1 spec) to start communication with the custom Host bridge device.
Poll the Empeg from the Host bridge device to see if it wants to talk. (This looks to be the simplest way)
Connect an Empeg serial port to the bridge to signal it wants to talk. (The tuner port may have control wires making this easier)

All the special software would be confined to the Empeg and the bridge firmware. The accessory Function devices should not need any changes.

I'm still looking for info on how devices are detected and how keystrokes are sent. one exploitable method for contacting the Host may be to make the Empeg disappear and return to the USB bus.

Granted for just a storage device this is all a moot point, there are ethernet devices that support USB storage media to be mounted as network file servers.