re: Where should i have my media server running and which one (plex,XBMC)

I don't know how much space you'd have available on that 214, but I'd think you'd be fine using that. I've got the 4 bay version that's a bit older, the DS412+ and I have Plex server running on it and it works just fine. I actually have an HTPC in the living room and I find that playing pretranscoded videos streaming from Plex runs much smoother on that PC than playing them directly from a share and transcoding them locally. You can try it out with minimal effort. Just install Plex from the package center, add a few movies to its repo and give it a go. Then your only issue would be dealing with how much space you'd want to dedicate to your media. It should support an external HD if you'd want to go that route FWIW.