Cheers, I was just wondering from what you were upgrading.
I think you'll definitely see a great improvement from the X-Fi Xtreme Gamer and T7900s, which, as the speakers are free, are an absolute steal for £46 total!
I kinda agree with No. 72 as well, though.
If it were me, I'd use those free T7900 speakers to make the most of the situation, and "settle" for very good sound for £46. The only reason I have the X-Plosion is because I got my SPDIF'd DTS setup for a bargainous price (used them with my nForce2 SoundStorm on my motherboard initially, so no soundcard outlay either) - you're looking at over £150 for an Auzentech X-Plosion and vaguely decent DTS digital speakers without finding a stonking bargain - plus, it'll take you longer while you either choose some speakers, or hold out for a bargain, while that X-Fi card could be with you next week. But you might be the kind of person who doesn't mind spending a few weeks or months doing that.
My two cents (yet again
).