Sound cards are... flawed by design. Static noise in the PC case disrupts everything and makes stuff bad. What you need is an external DAC. the Schiit Modi is a good one. (dunno about UK though). I'll leave the headset discussion to others. BTW, below is just a promo for charity if you care.
Folding@Home is a "distributed computing" project. It lets users "donate" their unused computing power to help disease research in critical areas such as Cancer and Alzheimer's. Do the world, the future, and maybe you yourself some good by at least checking it out. Link here. http://folding.stanford.edu/
Moral things aside. Many performance enthusiasts love to compare how well their PC is by showing their points tally for folding. Tom's Hardware...