It isn't possible to access content other than through iTunes.
Additionally if your photos are in iPhoto or Aperture, these applications may not function properly if the photos are not stored on a HFS+ formatted drive.
There are admittedly a number of people who think that being able to access content without iTunes is a good idea but few realise the features that would be lost if this was possible. There are plenty of other devices that do this if this feature is important to you.
Whether Apple will support this no one here knows but I suspect not, on the other hand we have yet to discover what the iCloud will mean for the Apple TV.
Is it possible to store all my photos and film on tne NAS and stream it directly to the ATV2 without a running iMac?
i'm using a DS411j as the home for iTunes library (no experience with iPhoto). i can shut my Mac down, then use FileBrowser on my iPad (or NetPortal for iPod Touch/iPhone) to access the files on my NAS, start a movie and use AirPlay to send the movie to Apple TV.
assuming all your media files are in the default location, simply drag the entire iTunes folder (not just the iTunes music or media folder) to the NAS.
when done, launch iTunes while holding the option (⌥) key, click on choose library at the prompt, and select the iTunes folder you copied to the NAS.
also, go iTunes > preferences > advanced and change iTunes media folder location to the NAS to ensure all future additions to your library are put there.
once all this is accomplished, make sure the share in the NAS is mounted on your desktop before launching iTunes.
edit: there's a blog on Macs and Synology here: http://macsynology.wordpress.com/. might be worth a visit.
I went the NAS (Synology DS) route with the goal of getting all my iPhoto libraries (new one each year) off the computer (filling up) and not having an external HD connected to my nice and neat iMac. That seems to have been a failing proposition. Even though I can use the iPhoto library, doing it over wifi has been a chore. It's okay on the computer directly connected via ethernet to the network hub where the NAS is. BUT, another goal of buying the ATV2 was to be able to show all of those spiffy pics of our son to the grandparents when they came to visit. I have yet to get ATV2 to play the photos that are stored on the NAS - even though all the home sharing stuff is set up correctly, iTunes is running (seems a dumb way to see my iPhoto library), and all the other settings. It simply seems to be unable to play the photos from the NAS - even though the computer can.
And don't get me started about not being able to play any of the hundreds of avi movie container/files produced by our Canon PowerShot camera. Movies that play absolutely fine on the iMac with no special software (beyond quicktime).
My NAS is becoming more and more a place to just do backups and the mergining library functionality shared between multiple computes and iOS devices seems to be a lost cause. very frustrating.