FWIW, I'd start by unplugging everything from the amp, and seeing if the noise is still there. If so, it's amp self-noise and you'd want to reduce the amp's gain, if you can, to get it into unobtrusive levels. If it's not the amp, I' d keep working backwards. Unplug everything from the receiver and see if the noise occurs. If it does, it's from the receiver, and you'd have to fiddle with output levels (channel levels) to see if you can get it lower while still getting adequate gain to achieve your desired listening levels. There's almost no chance the digital connection to from the computer adds noise, so if it's not the amp and it's not the receiver, it's the interface.
Of course it might be the multiplicative effect of a little noise everywhere, in which case, for home use, experimenting with relative gains is likely the best way to find the quietest quiescent noise level . . .