Let's try to put this discussion on the right track. (There doesn't seem to be any posts here from people who actually design analog circuits.) The SO post

Let's try to put this discussion on the right track. (There doesn't seem to be any posts here from people who actually design analog circuits.) The SO post reduces to comparing two versions of noise: One from (A) software control of the DAC and the other (B) from hardware. (A) Pretend that everything except the DAC was noiseless: The noise would be due to the nonlinearities and quantization in the DAC. (B) Pretend that the DAC was perfect: The noise would be dominated by the noise-equivalent input-power introduced by the resistance present in the components (including the transistors used for amps). In short: (A) is a function of how wide the range of bitcodes that you use. The smaller the range, the larger the noise component relative to the signal. OTOH: (B) is a function of temperature: All of the noise power before the final dial to your amp is passed through as is the signal, so the ratio stays constant. There is also a constant noise power introduced after that final amp, but I would guess it is negligible compared to the amplified noise power. So tl;dr = For a decent sound card, maximize the software volume and then use the analog dial.