Charlie is absolutely right. If Exclusive Mode is enabled, the PC setting is irrelevant. However: In case you should feed your DAC with a sample rate which it does not support you will get an error message since up or down-sampling will not occur to adapt sample rate. But that is of minor importance.

Use Exclusive Mode, WASAPI Event with about 40ms of latency, set software buffer size to about 5 seconds, use High Thread Priority and MMCSS in Mode Audio. I have made very good experience with the Foobar Explorer combination in that way.

If you want you to do another favour load down RAM Disk and and load your playlist inside your RAM. As already said before take care that Replay Gain is disabled.

I have to state that the finding with the volume slider was quite tricky, well done. But it's clear: That volume is digital. So it uses DSP and hence prevents bit-perfect playback...

Sascha