You may want to upgrade to a DX or D2X, although to be honest, you probably won't see a huge benefit in doing this.
If you actually want to upgrade to see a noticeable difference, you're probably better off looking for some new headphones and upgrade to something like the STX or STX II, or alternatively an external solution - but of course all of this is going to cost quite a lot more than £100.
You're pretty limited since your headset is 5.1, and USB powered.
