[SunshineReggae]

with a soundcard's HO, except potential clipping(nothing tells that there will be any), everything else will probably work better close to the max volume level. for a better SNR and also to avoid using too much digital volume.
clipping is usually audible so if you hear nothing at max level, you can be pretty confident with say 85 or 90% max volume on the computer.

but I'd say, go get a cheap usb dac, even a 20$ hifimediy will probably best your soundcard on HO. and never think about double amping again.

 
Thanks

It's not my personal practical situation by the way. I'm just curious to find out how things work in theory. But about the clipping; I guess that'd only happen if one hooked up headphones that exceeded the sound card's ability to deliver enough power, right? So if I hook up another amp to the sound card, clipping is not likely to be an issue. And the reason for that is that headphones have different requirements than, in this case, a second amp in the chain would. That is to say, the second amp doesn't really have requirements, since all it does is amplify whatever it's given by the sound card. Is that correct?