Ok, back up a second...
I didn't know WTF an "offramp" was, so I looked it up. It's just a network interface to a DAC. Runs only via iTunes and limits you to two or three file formats.
So that means you'll also need a computer -either a PC or a Mac - on which to run iTunes. The Infrant NAS is just a network _file_ server. They've jiggered it to run SlimServer if you want (trust me, it's so slow that you don't), but other than that, it's primary purpose in life is just to store files on your network.
Are you sure that's what you want?