Matt,
I am going to have a full day listning session with the Dartzeel Ethernet dac/Integrated amp (the one soon to be released) in 2 weeks, i will let you know.
USB stick is a no-no for ultimate performance and NAS(ties) have too many issues in terms of signal degrading connections. Packetized data gives problems.
Ultimate performance (IMHO- informed by some insiders I know and respect) will come from optimized SSDs and SDXCs, BUT not sure they should be in the dac box. Given that, all this may end up in the speaker, like Linn Xact, Devialet Phantom or Goldmund Metis lines.
What does Linn Marketing say? The speaker IS the source. LoL
Just MHO and food for thought.