Well I can confirm the problem appears to be specifically firefly & wireless.
I did have a wireless - wireless connection going, Laptop to 802.11n AP, wired to ADSL router, then 802.11g to soundbridge. I would randomly but regularly get the message "The Media Library has shut down" and playback stops. it however is still immediately available in the subsequent screen to select library. Really frustrating when listening to podcasts because you cannot fast forward to point in time!
Going from the laptop, wired to 802.11n AP, wired to router, and 802.11g to roku does appear to work fine.
There is *nothing* else happening on my LAN other than me streaming to the Roku, so network congestion is not an issue. I think I have narrowed the issue down to mDNS broadcasts going awry.
Just about to see if the problem continues by turning on itunes library sharing in iTunes and seeing what happens....
*update* Confirmed this happens with iTunes sharing as well. I guess its time to bump that idea of a NAS up the priority list