Is an amplifier really necessary ?

[djkvg]

you're plugging the RCA cables straight into your computer? are u mixing using your computer or using CDs?

[Andrew B]

I thought about some krk speakers, like these http://store.apple.com/ca/product/H7526LL/A
Good idea ?

Yep, just plug them directly into your mixer. No reason to go through a computer.

As was said, look elsewhere to buy them.

[KLH]

^ Great seeing you again, Andrew B.

The only thing that I'd add is to realize that NOT using a high-quality sound system tends to make music sound good enough when it may not be when played through PA speakers. ALWAYS remember to keep your music as high-quality as possible.

-KLH

[DJ Highline]

You will always need an amplifier...the question is where is the amplifier located? Is it internal (powered/active) or external (non-powered/passive). Almost all computer speakers are powered and you can just plug right into them. But this is an idea you should keep in mind when you look to get bigger speakers. One is not better than the other just different.