Way to go for best sound quality?

My friend owns a desktop computer running Windows XP with Creative Sound Blaster X-Fi Elite Pro sound card. He has been using a pair of Yamaha HS50M speakers and Sennheiser HD-580 headphone. He would like to get the best sound quality through his speakers and headphones. Does he need to change the sound card or is there any easy and cheap way to go?

Thanks in advance.

He's already got 'easy and cheap' - sure as hell hasn't got 'best' though, not by a long way. He hasn't even got best value; most of us wouldn't run anything Creative Labs made as a matter of principle, never mind anything else, because they have all sorts of internal issues - like resampling everything to 48k, whatever it is.

If he wants a better internal card with less issues, then strangely enough, one of the companies Creative owns, E-mu, will give you a considerably better performance, although you have to get one of the more expensive ones (1616m) if you want a headphone output. At least we know that E-mu kit actually works properly, and delivers very good performance - you have to pay stupid money for better, and it's only fractionally better, even then.

I use a Maya44 and I'm happy with the sound it gives me.
 

best sound quality .....cheap

Sorry, but these two simply do not belong together.