squeeze for Edifier S530D or Corsair SP2500 or Harman Kardon Soundsticks III or Creative Gigaworks T3 or AE Aego M

or maybe upgrade your Edifier C3 to C6 (aka HCS5640)
Edifier DA5000PRO oso not bad

what I've recommended there is around RM700-800 range for your ease.

Performance wise of C3 vs. C6
C6 performs better overall especially in terms of subwoofer power and crisp clear refined trebles (unlike C3 plastic sounding trebles)
I tell you the mids are thick and full of power

S530D on the other hand, performs differently (in a good way)

I don't know about performance in 5.1 but

HCS5640 can work very well for bassheads (recommended for FPS games or rumbling movie explosions)
you can set the HCS5640 speaker/subwoofer ratio to reduce the volume on sats and increase SW and overall volume, giving out more powerful subwoofer depending on situations like movies and games
almost as powerful as logitech speakers but with tighter bass
you can almost mute the satellites and leave only the sub bumpin hard and vice versa if you want only the satellites to work
the S530D can't do that much for bassheads... satellite power maybe a little too powerful sometimes (only sometimes) leaving the subwoofer weak and useless on large areas (I didn't really cared much about this part though)(it performs well with games too)
but do note in terms of clarity I'd prefer the S530D over HCS5640. So test it out first before getting one if possible.

much more powerful compared to C3 with instant win...
you get double the bass, subwoofer and satellite bass

(might get muddy if satellite got bass but meh, I like how it sounds this way )

I suppose yea?

yea... built in iMac soundcard (no soundcard how to make sound eh?)
good enough. But there is room to upgrade (I find myself enjoying these with my Hippo Gumstick music player more compared to the iMac sc)

so which one are you deciding eh?

nope... totally different taste and style

oh noes... totally different too
VS4121 bass is muddy and crappy... (the old ones are the good ones, new one sucked)

this(HCS5640) is tight goodness full with yum yum

The Hub, Viewnet got those speakers if i'm not mistaken. Don't forget to checkout at All IT and Sri Computer also 

S550 gets awesome mids and clarity
Z-5500 gets better functionality for more computers with less mess

S550 got tight bass, Z-5500 got boomy louder nightclub bass

it's either Edifier S530D, Corair SP2500, Logitech Z623,Creative Gigaworks T3 or Harman Kardon Soundstick III

ask your ears.

my choice, Edifier S530D... but that's my choice and I may be biased because I like Edifier

Finaly i bought Logitech Z623 YeheY!!! Very satisfied..

My ears vote for S530D 

my s530d cant hear the bass if near the woofer,i need stand 2meter like tat oli can hear the bass.. 

That will be a huge upgrade from your previous system. Also, that will burn a deeper hole in your pocket.