Cant comment on S530D but Aego M is very very highly regarded for its musicality. A sound card is used to process digital sound into analogue signal for the speakers to play. If you are seriously considering such good speakers then yes, you need it. Onboard is terrible waste of those speaker's potential. Cant comment on which SC to get as im outdated. Price wise maybe something in 300-400plus range as an estimate.

hi there, i'll give some of my opinions. hope it helps.
1. not sure about this. sorry.
2. this was elaborated by another forumer. just wanna add a few points. there are 3 things to consider.
    a. the number of channels (speakers), e.g. 2, 2.1, 4.1, 5.1, 7.1. the ".1" is the subwoofer.
    b. external or internal. for me, just go for the internal cheaper and equally good.
    c. the quality and type of the analog-to-digital converter (ADC). normally indicated by the bits. generally, the higher the bits, the better the quality of the sounds.
3. depends on your budget. if you are planning around 100++, then i would suggest Creative SB Audigy Value, around RM115ish. internal card and supports up to 7.1. if you have more to burn, then go for Audigy 4, supports 7.1 too. these are the SoundBlaster series. for the pro series, you can go for X-Fi series like Fatal1ty. Audigy value and 4 supports vista but check on fatal1ty before buying. Creative has some issues with a lack of Vista drivers.

the thread state RM390...market price wont be so cheap