Thanks Jim,
I have been looking at various amp/dac schematics and seen all sorts of solutions from direct grounding to resistors, caps/resistor in parallel, diode pairs, and even bridge rectifiers/resistors/caps in parallel. Seems everybody has a differenent answer to the question. A low value resistor did seem the most popular so i might experiment with that, and i should have some inductors salvaged from ATX power supplies, in fact i know for sure i have seen some in the earth wiring circuit now that you mention it. I'm still really conflicted on if i should bother with ground reference at all to be honest.
At the moment i have the +, -, and chassis earth totally isolated from the PC itself by means of a USB Isolator board (pic below) so in my case the grounding will only be connected to the casing of the PSU box. (DAC in separate enclosure)
As for SQ, there is a considerable difference IMO. For me it was the smoothness and full bodied sound of bass guitars and drums that was immediately obvious, and after more time listening i noticed the high end frequencies are much cleaner and better defined.
On a somewhat related note, this is the quality of the USB 5v power i started with, hence my journey into a dedicated supply... Just how noisy is a switched mode power supply? - diyAudio
