In need of NAS (and media player) server OS

I am in the process of building a NAS, and I am now in need of the appropriate OS. Here is what I am looking to do with it:

Primarily:
- Act as a shared file store
- Play music to my stereo
- Be able access its files from outside the network
- Automatically backup specific computers in the network

Secondary:
- Connected to my TV, watching hulu/youtube/etc.
- Possibly host a website

For the playing music element, I would connect this to my stereo with the hope of playing music straight from the box (no squeezebox, etc). I just need a way to remotely control my playlist. I've seen some plugins for Winamp, but I'm not sure if there's an easier way.

I have only beginner Linux knowledge (for instance, I can SSH, but don't know much command line code), so that is a factor in my decision. I've tried Amahi before, and appreciated the simplicity of installing and getting it running, but maybe other options are just as easy. I know of FreeNAS, but I don't think that will suit my needs, due to the media element of the server. The other one that's hit my radar is Ubuntu Server. Would that be easy to configure, and could it play media files to my stereo or TV? I do really like the Webmin part of Ubuntu, from what I've seen. I'm rather drawn to that type of interface and customization.

If anyone has other options on OS's, I would greatly appreciate the input! Also, if there are ideas for remotely controlling a playlist, that would be great too. Thanks!