just use normal volume as u listen.
desktop can.
but i suggest u just use it normally
it will burn in itself.
and plug ear phone into desktop sound card isn't really recommended. as sound card often have obvious DC offset.
except you only plug the earphone when your computer had load into window. and unplug it before u shut down.
wanna know what i mean. u can plug a speaker on the compter, turn the volume to half.
and see what happen when you switch on and turn off the computer.