Does the Korg d1600 have mic preamp or d/a converters inside that would allow me to use this piece of equipment as an audio/midi interface? I believe It has all the appropriate inputs and outputs?
The Korg D1600 has a comprehensive list of inputs, including mic preamps with phantom power. But I see no mention in the manual (linked below) of being able to use it as a computer interface. The words 'USB' or even 'Firewire' do not appear in the manual. So I'm afraid your answer is no. It is essentially a self-contained recorder.
You can use it as an input for all your devices (mics, synths, guitars) and then plug thru the S/PDIF optical output. But you have to have a bacic sound card with optical S/PDIF. If you have an old computer you can use M-Audio Firewire 410 (drivers are only available for older operating systems like Win 7 etc). You can record only 2 tracks in real time. But you don't need to plug and uplug your devices again and again if you use the Korg as an input. Korg also has great effects which you can apply during recording process.