Ok so basically I have some decent speakers; Acoustic Energy Aego M 2.1 (for PC speakers anyway)...and I purchased recently some Grado sr60i headphones which sound fantastic, very impressed.

I was really planning on using the speakers during the day and headphones really for 10PM onwards when everyone else in my house is fast asleep, however I've started using the headphones alot more.

I should really just say simply how can I get good headphone sound from my PC but I feel a justification needs to be there. In the computer at the moment is the Creative X-Fi xtrememusic, but I used to have a fatality pro which I replaced because it become faulty but can will easily say they both sound pretty much the same through the headphones anyway. On the sound output I use completely neutral settings which may be a reason why, so I turn the x-fi function off, the equalizer, and the EAX/3D effects are only enabled for gaming but I mostly listen to music anyway.

Testing the headphones on the hifi gear downstairs, albiet 10 years old now and only Pioneer they still sounded alot better but why...? I can't put into words other than it was a more relaxing listen even though right now I'm listening to the same CD through the computer for testing reasons. The sound seems more 'forced' than it was through the hifi's cd-player headphone out? I really cannot put it into words, and it's mainly because the difference was subtle but to me noticeable.

So really I would like advise, I usually buy equipment thats 'good bang for buck', I'm not sure exactly what needs to be purchased for the computer...a better soundcard? a headphone amp? both?

Advice appreciated anyway.

I have the same soundcard as you have. My headphones are some sony "studio" headphones, not the best ever probably, but they perform very well.
When i compare their sound i get with the computer, compared to the hi-fi system in my living room, there is a difference like you described.

I'm not sure what would need to be done to improve the sound quality with the computer, but i think the reason why it doesn't sound as good as the hi-fi equipment is...
The soundcard did cost 100 bucks, while the hi-fi system (the amp is the big difference IMO) did cost a few hundred bucks (doesn't matter if it's 10 years old).

A cheap soundcard will never sound the same as a halfway decent hi-fi amp.

Maybe a headphone amp would help indeed.

The cheaper soundcards get, the more they "color" the signal they output. It's all about the D/A converters and other electrical components on the board.
I do think getting some headphone amplifiers will help to "warm" up the sound but that still doesn't get rid of the altered tone. You could then also try to turn on the software EQ and play with it until you like it.

The best thing you could do to match the sound you get from your hi-fi is invest in a much better sound card. Although this can be expensive, it's the only way.