i have the exact same problem i think its a common one mate, i found if i put windows volume above half way it goes crazy with the buzzing and distortion same with the volume on the headset.
try putting windows to 4, amp as high as you want and headset volume to 5-6 and it should be crystal clear although if its like mine the vibration wont work anymore.
another annoying thing is whenever i go speakers i have to go turn windows back up becuase my samsung cinema thing really doesn't like it when its half way :S
should work though, good luck