I'm not sure how good you are with messing with the Synology, but there's a pretty easy way (assuming you have half an idea of what you're doing) to deal with this. Go to Package Center on your Synology and download 'Audio Station'. Go through and get it all set up. It's not complicated. Just make sure you give whatever account you're using the right privileges .
Next go download 'DS Audio' app from the iOS app store. Since you've accessed Synology on your android, I'm sure you already know what to do here. You can access and stream/download all your music on the Synology through the app this way. I do mine another way (more on that in a minute), so I don't know about now, but in the past, the app's performance was not the greatest (though I have a lot of music to be fair). I just messed with it a bit and it wasn't too bad, so maybe they've improved it since then.
Somebody above mentioned Subsonic. I've been using Subsonic for quite a long time now and I love it to death. I ran it off my desktop for the longest, then it (desktop) started acting up, so I did some looking and now I run Subsonic right off my Synology. Works great for me.