Seekburk,
I am also using Mac Mini as music server with Amarra mini and Ayre QB9 Dac. Because of the need for decent looks/ergonomics I decided on 2 - 1TB Iomega Minimax external hard drives - connected using firewire 800 and daisy chained with Raid (mirror) set up. This provided one drive for playback and the 2nd for back up.The drives are extremely quiet, error free and look good stacked on top of the Mac mini. Cost at Apple Store was minimal compared to other options (NAS) which have been known to be problematic. You can check them out at the Apple Store online.