Dolf,

Don't know if you you are aware of the Sonos forum - there are many threads about NAS, RAID boxes etc. I think most quality NAS will work. I had a Maxtor which was fine until it died (which entailed a lot of reripping), and now I have a QNap. Once set up, both were pretty much no maintenance. I would choose a cool running and quiet unit.

Main system (when room is done): 861v4, 7 x DSP33, SW1600, Oppo, Sonos