Building Router - no port forwarding possible

[rikcloet]

I live in a big building where I cannot install port forwarding on router but I want to use DS Audio on my tablet.

I can use DS File because it uses EzCloud ID and Quickconnect, that works very nice, so it is possible to connect to my NAS from outside! Why isn't it possible for audio and photo?
Is it a feature that Synology can program in DS Audio and DS Photo too?

Hope someone understands my problem