Well, bit the proverbial bullet and got myself a 5.1 system today. Went with the Samsung HT-TZ325, very similar really to the one in the OP but supposedly a bit more powerful and has a few other pointless features. Same price though so can't complain.
Rather nice so far, it's not the classiest looking thing ever and I'd have expected a £200 set to have a somewhat better finish, but it sounds good. Bit of effort to set-up and get working properly, and the manual isn't quite clear about what audio formats it supports via optical. I've selected Dolby Digital 5.1 and DTS 5.1 on the PS3 and having given GTA4 a go just now, I'm getting proper surround sound effect so it's obviously working, it'd just be nice if the receiver itself would acknowledge or display something to verify.
Going to give Uncharted another play-through now just to tide me over until the sequel arrives, so it should be quite a cool experience with some decent speakers now!