Joc,
I am am also using a Cullen modified Sonos ZP-80. I use a Buffalo Teraserver NAS drive, attached to my half wired/half wireless network. Like Stevenstone said, your PC does not have to remain on with an NAS device, only the hub or switch needs to remain powered up. Some of my Sonos units are hardwired and others are not. I've not been able to tell a sonic diference between the wired and wireless connections. The Teraserver is RAID 5 configured right out of the box, so the data recording is already redundant, not really requiring any other backup.