Spencer, hard to pin down why, could be that Fire Wire is better than USB, or the USB interface in the Dac8 is inferior to the Weiss interface, maybe even the addition of a extra clocking between server and Dac . the volume control within the Weiss is better so far than the volume control within Foobar or the Bent Passive Volume control I tried or the volume control built in to my Vac power Amp. I also tried all the above in combination with each other.
I haven't tried your microRendu , not sure it's available here, well worth looking into though.
I have assumed that once bit perfect with low latency was achieved there was not much more could be achieved but I am open.