I now almost exclusively listen to file-based music sources, and I can tell you from personal experience that the USB port in the 990 is indeed more than capale of serving as an external soundcard.
I am not familiar with the ready share capability of the netgear router, but I suspect that is something like a fileserver appliance. If so, you will need another device to turn those bits into a "sound signal" (notice I did not say sound). An old laptop or PC can do the trick. That is unless, of course, the netgear router has this capability already built-in.