Can I plug my powered 2.1 desktop speakers through my E7 "soundcard"/amp/dac?
I'd rather not fuss with multiple sound cards/devices in Windows if I don't have to.
Sure. Just plug it in via USB, and plug the headphone jack for the speakers into the the Fiio. You may just have to go into control panel > sound and tell Windows which output to use, but it isn't hard to configure.