David:
Running REW graphs and using the same mic, converter, amps, and speakers WHEN the DAC is changed, the response is significantly different -- mostly in the midrange. The 3 DACs checked so far include the Sabre 32s in an Oppo 105D, an Emotiva DC10, and the aforementioned RME UFX. Can provide graphs if you are interested. Suggest this might be the result of the analog electonics after the DAC's chip, but this is just a guess. You can, BTW also hear these differences when REW does the sweep.