Yes i will be listening solely on my PC. I got an ASUS Maximus V Formula with great on-board audio. The audio segment is separated from the rest of the motherboard, which prevents electrical interference and hence, better reduction in noise, etc..
EDIT: i should mention that my on-board audio, however, just can't push these headphones at all :(
The headphone amplifier chip used in the Maximus V Formula (Ti 6120A2) is the same one used in my Essence STX and it can drive 600-Ohm headphones. So i'm surprised it's not doing a good job driving 250-Ohm headphones.
Looks like the audio processor is a Realtek.
Might try updating to the latest drivers.
Maybe check your BIOS setting.
Is there a gains setting for the headphone amplifier?