Hi mate,
I’m neither a Firefly or an iTunes expert, but i would imagine that as with most VPNs, yours is being treated as a ‘gateway’ – meaning that as far as iTunes is concerned, anything beyond a gateway is on a network outside your LAN, and won’t go looking there. Kind of like why you can’t find any Firefly servers that are on the internet – because they’re beyond what your client sees within its local subnet.
Of course you can ping and get to the web interface, because you’re defining an address outside of your LAN – whereas iTunes probably just looks around what local resources are available to it.
I could be wrong though!
Regards,
Justin