Imkhawx, It s great to hear your enthusiasm with your Decware. Seems to do that with a lot of us.
As to the ZDAC playing from a server, there has been a lot of experimentation with DAC's toward the end of analog presentation from digital, and with substantial success. And though there is thought that computers only produce 1s and 0s, this has empirically been soundly disproved by those who have explored.
To optimize the computer as server, there is the real necessity for specific computers, how they are set up, the feet they are on, the power cords used, weight on the computer, the USB, coax or toslink cable used.....just like with amps, these things all matter. And in my experience, they still matter with an Async interface which is thought by some to rule a lot of this out.
Then there are files. Presumably, your iTunes files are compressed in some way. I have found that error corrected, uncompressed files are distinguishable even from so called lossless files, and that all the forms of heavy compression can sound pretty good with ear pods, but through your taboos.....this is very different.
So finally, if the objective is to get really good sound from the ZDAC, it is apparent that stuff other than 1s and 0s comes through those cables and from the computer itself, so the considerations are as complex and dependent on synergy as with the rest of our gear.
If you want to look further, there is some discussion in the ZDAC area of this forum, and a great deal on this
http://www.computeraudiophile.com/ Check out the FAQs
Or if you can skim through to find the kernels of wisdom, the DbAudioLads folks (tranquility DAC) have done extensive explorations with the server/setup/cables/arrangements etc...... the whole objective being to match or beat vinyl in analog presentation of music. Also, your ZDAC was designed by a Vinyl head, so Steve worked hard to create the possibility for an analog presentation. To get close to it may take some exploration though. But anyway, there is good stuff in this thread if you are interested.
http://www.audiocircle.com/index.php?topic=74816.0Have fun!
Will