caesar,
Roon is able to find the files on your NAS, but it does that through your computer's network stack (regular file sharing). The benefit here is that you don't need extra software on your NAS for Roon to "see" your files. Once cataloged, Roon can read/write them as if they were locally on your computer.
The Aries, and other network players, rely on a different protocol, called UPNP/DLNA (or its extensions such as OpenHome). That's why you need extra software running on your NAS, the UPNP/DLNA server. Examples of such would be MinimServer, Twonky, Plex. That server will scan your NAS for music files, and make them available to other UPNP/DLNA devices on your network (such as the Aries).
So far, and AFAIK, Roon can't see UPNP/DLNA servers (to fetch the files), and it can't use UPNP/DLNA players/renderers (like the Aries) either, to output the music to.
Ideally, we'd be able to do just that. Use Roon only to cataloge, organize and tag our libraries, while hosting them on a NAS, and playing everything through a dedicated streamer.
alexandre