Hi,
As far as I know, there is no NAS where Subsonic is a supported package from the NAS vendor.
For Synology, there is a 3rd party package, available from a non-Synology package source - here is the package sources I have setup:
http://www.cphub.net/http://packages.pcloadletter.co.ukhttp://packages.synocommunity.com(I don't remember which one has the Subsonic package)
Last time I looked, the Subsonic package was v4.8 - i.e. Ancient, and you'll miss out on good features, possibly also Sonos integration (don't remember when that was added).
Unless the third party Subsonic package has started getting updates, I wouldn't go that route myself...
Recently a guy posted about a Docker-image for subsonic in these forums (I think it was in the "Mods, Apps and Clients" section).
The Docker-solution probably requires a reasonably high-end NAS,
and is also dependent on the maintainer of the Docker-image for updates.
As I wrote, I'm using the Tomcat+WAR installer on Subsonic.
I have been quite happy with it: it only depends on the Tomcat package which Synology maintains, and the WAR package which comes directly from Subsonic.org.
Upgrading Subsonic is easy with this setup:
- Stop the Subsonic service in the Tomcat manager
- Undeploy subsonic from Tomcat manager
- Deploy new subsonic WAR package.
- Start the Subsonic service.
- Rebooting the NAS seems necessary though.
As for which NAS to buy... I can say my experience with Synology has been good.
If you go for a Synology, getting one with an Intel-based processor will be best (but not cheapest).
Many 3rd party packages, and also Synology packages, are only supported on Intel-based systems.
If you are going to use transcoding for Subsonic on the NAS, getting a 2 or 4-core Atom-based CPU is recommended.
Depending on the number of simultaneous users/transcodings, you may need to go higher CPU-wise.
For a smaller setup (family+a few friends, a 2-core Atom-based system works fine for me).
I'm not aware if transcending will be necessary for the Sonos integration.
Hope this helps a bit

Michael.
Developer of play:Sub for iOS.
https://geo.itunes.apple.com/us/app/play-sub-subsonic-music-streamer/id955329386?mt=8