Speakers and sound for FSX

Does anybody have a suggestion for speakers for FSX. I use my headphones for ATC and the speakers for engine and environment. If I play my engines in my headphone they sound great but thru the speakers it is so so. I tried a different set a speakers but they were too bright and the ones I have now aren't bright enough. I have played with EQ and such but can't find the sweet spot. Is onboard sound good or should I get a sound Card? Also the speakers I'm looking at are the Logitech z623. Right now my speakers are Logitech Z313. Music and other things sound great it is just FSX that doesn't sound that good. Any suggestion please. Josh