Your used DAC3 is worth about $1600, so I don't think that I would invest another $2000 into it, you'll never be able to recover your investment. I would personally rather put that money into a Music Server or Logitech Transporter.
If I were you, I would leave the DAC3 as is, because I think it's great, and then when you're ready to jump into the Higher Resolution Audio Formats 24bit/192kHz, you could sell the DAC3 for $1600 and then add your $2000 and see what you could get in the Music Server/DAC $3000-$4000 range that can handle 24Bit/192kHz Audio.
Excellent advice and very obviously the logical approach. You really need to check out some of the latest offerings by companies who are making great headway in the development of digital playback and the different methods that are available for executing computer audio (i.e.: computer-based, component-based/network server-based). I recommend visiting this site,hereto learn more about implementing high-end digital. I think you can better invest your $2,000.