Bigger watts doesn't mean better sound; nor does it mean better speakers.

@Killer Tomato
You've just said 2.1 is good enough, so may I ask why you're going for 3.1? (Left, Right, Center n Sub)?

Here's my 2 cents: Use all those money on a decent pair of 2nd hand bookshelf speakers.

Yup, 3.0. Well, I've my reasons for ditching the center speaker. W/ my setup, center speaker mess up the stereo imaging @ sound stage. I don't know how to better explain this, so hopefully this short article that I just found could help.

As for why 2nd hand, IMHO RM300 couldn't get you a good brand new bookshelf. With 2nd hand speakers, you could at least get a decent@good entry level bookshelf speakers.

p/s: Since you've changed your choice from multimedia speakers to HiFi stereo, guess further advice would be better asked at the HiFi recommendation thread. Besides, the pros there should be able to give better suggestions than me.