Ever since the Cobalt RaQ4 (and its 450 MHz AMD K6 processor) became obsolete, I've wanted to hack one into a drive bay / iTunes controller. When I started running out of space on the Mac Mini which serves as my living room media computer, it gave me the kick in the butt I needed to start the project.
Step 1: The Plan - The Prep
First, I wanted to use Thunderbolt as my drive interface, so that I'd never experience any performance bottlenecks as a result of my connection, and also because I wanted a forward-looking technology (rather than Firewire, which is clearly on the way out). I already had some SATA drives on hand, so I decided to get LaCie's eSATA Hub. At $200, this was the priciest part of the project by far. But as I've said, I was going for speed. A pair of SATA to eSATA cables ensured I was able to connect my drives to the hub.
My second goal was to make the resultant device as "authentic" to the original as possible. I wanted the LCD, the lights, and the buttons to all work. I decided that: a) the buttons would control iTunes and the volume, b) an LCD would display the current track, and c) the status lights would be replaced with a music-responsive, colour LED lightshow.
I decided to keep the original RaQ power supply in order to power my drives (with the help of some molex to SATA power adapters). Everything else was stripped out.