spend on the streamer or on the DAC ?

I have not listened to ethernet vs. usb myself, but I have two local dealerships that I like, and both don't like usb connection.  My own system, Naim 555 server and uniti/core ripper and storage, is ethernet connected. 

The Naim has the server and DAC in one box, but they do go to extremes when it comes to internal isolation.  First, there is a separate power supply box which has multiple power feeds coming from the box to isolate the feed to the various functions in the server/DAC.  The DAC is isolated from the rest of the server by being in a faraday cage; to enter the cage, the digital signal is converted to an optical signal.

My local dealer, who puts together some very expensive systems, usually recommends the Sonos or Roon streamer.  It is not uncommon for his customers to have Sonos feeding an Audio Note DAC5; now THAT is a massive price discrepancy.

twoleftears,

I agree with you. There are advantages, at least theoretically, for coupling the two together.  I have a Naim 555 server/DAC combination.  Different sections of the combined unit are served with their own power feed from the separate dedicated power supply (separate box).  The most noise sensitive section is enclosed in a faraday cage.  In order for the digital signal to enter the faraday cage, it is first converted into an optical signal so that the signal passes optically into the faraday cage (noise/rfi cannot come in riding on an electrical feed).  This sort of complete engineering makes sense.