Just a quick google, as good an explanation as any LessLoss - Volume Control Option

In the digital domain prior to D/A conversion.

This is the worst way to control volume level. You not only loose bit-depth of your signal, you also introduce rounding math errors, and ultimately reduce the signal/noise ratio of the actual conversion process. You do not utilize the DAC chip in its best operating conditions, and receive a distorted output signal as a result.

No Darling, I've had it months!