Reply to sound problem with my S4

bought an S4 a few months ago. I'm slightly worried that I've already killed the sound card though :/

since its new and I want to get really comfortable with it first, I've only been rocking it in my room, so Ive been using the headphone jack to listen to everything. but Ive noticed the sound is actually horrible now. you can notice it mostly when its just a bassline and kick (like when an electro track drops), and you get all this not nice sounding stuff happening in the top end that really isn't there when I AB with my onboard sound card. its like distortion crunch, but worse, really unmusical.

I also quite like blasting it at full gain regularly (cause louder=better obviously), and after speaking to a load of people, they said you can kill a sound card by running it at full gain. so now I believe this is what has happened.

what do you believe?

if this has killed it, will it affect the main outputs or is the monitor bit separate to the main outs?
andddddd, if so, why do they allow sound cards to be turned up to a destructive level?!?! :S:S


hope you can help. as you might imagine, I'm quite annoyed having dropped like 750 on this..