So I have enabled UPNP (or Port Mapping as Apple calls it) on the TC. This I have done.
Just to be clear.. Apple does not support UPNP .. and port mapping is not the same thing at all.. when you map a port it is fixed.. UPNP is automatic system that opens ports when required but can negotiate ports which a fixed mapping scheme can never do.
All of this is irrelevant.. upnp and port forwarding or mapping is entirely to do with remote access to files over internet.. and the plague of NAT.. which is how the router connects us to the internet.. This is not used in local lan where all ports are open by default. You can remove your port maps.. they are meaningless in this setup.
But no matter what I do I cannot browse the audio files on the shared section of my TC using the app.
There is no media server in the TC.. it is nothing more than a dumb box.. it stores files.. all the smarts must be handled by the software on a computer or iOS device. Or the media player.. which I take it the DAC is not.
Basically I just want to the DAC to process my library of FLAC and ALAC files stored on the TC as they are too big to store on my iPhone / MacBook.
Your player is most likely a streaming device.. it cannot see the files. Nor can the TC stream them.. it has no brains at all.
You must connect to a computer or a smarter device than a TC.
Now I don't know the product.. so just a quick look it says.
In addition you can use AirPlay with iDevices running iOS7, to send music to your Hi-Fi system from Internet radio services like vTuner and TuneIn Radio, as well as music streaming services like Spotifyand Qobuz.
The airDAC is one of the simplest ways to enjoy your favourite music from your UPnP device, iPhone®/iPad® or computer running iTunes® and brings Arcam quality sound to a whole new generation of music lovers.
I think it is important for you to understand.. a TC is NOT a upnp device.. mapping ports doesn't make it one.. and this mixup of terminology is not helping.