Cwlondon, I'm not an expert so take what i say with a grain of poop.
I've read that a 2.4GHz pentium is recommended for playing audio to handle upsampling properly. Other than the processor you have a hard drive (any will do as long as it's quiet and reliable and the right size for your collection) the dvd/cdrom drive (any decent one will do), the sound card and various programs. So any computer that has the right processor will suit your needs. (You pay more when a computer is loaded with software, obviously, and you don't need much in that area for your application.) Therefore, the creation station is overkill but not a waste. It's quiet, reliable and has great customer service (you should call sweetwater with these questions, btw.) I would suggest buying what is most quiet and looks the best with your audio gear if paying an extra grand or so is not a problem. if it is, look into other computers as options.
Regarding interface. I think what you're asking is whether or not you'll need a sound card and the answer is yes. Do you need a good one? This is a question for someone else. I went a different direction. After reading about jitter the best theory (theory becasue i haven't heard it) seemed to be Steve Nugent's (empirical audio) "Off-ramp I2S" - this connects between your computer and dac and significantly reduces jitter. It's an elegant solution. You do not need a sound card in this case. Basically, it is a sound card. Once i read about this device i stopped researching sound cards. The I2S is a connection that your dac doesn't have. Steve adds this connection to some dacs like the Benchmark Dac1 (this is what i went with.) I don't know if he can do it to your arc. Anyway, i'm waiting for mine and it's going to be a LONG wait but i'll let everybody here know the results.
