|The human ear cannot hear digital sound; only analog sound. |
Thats very observant of you. That why all sounds come out of a loudspeaker or headphones which are analogue devices. If you have an amplifier with digital input I would use it, after all, if the sound is being produced by a computer, whether it is digital or analogue output, it always starts of as digital. The only analogue sounds sources are vinyl records or tape. Best to keep it digital and just do one D-A conversion in the amplifier before it is fed to the speakers. The D-A converter in an stand-alone amplifier is likely to be of far batter quality then one in any but the most expensive sound cards. The beauty of digital signal processing is that it is less prone, almost immune, to interference where analogue signals a very prone to interference.
If you have a hum it has nothing to do with whether it is digital or analogue, More to do with a miss-match between the ground of the computer and the amplifier, inducing mains hum. That can usually be cured by taking a ground wire from the chassis of the computer to the chassis of the amplifier so that both devices are at the same ground potential.