i have both, i can hear the difference. sound blaster also lets you customize the sound more.
though really i suppose it would depend on you and your speakers. put it in, listen to the difference. if you cant hear one, pull the card.
my 5 cents: Although I have only Genius SW-HF 5.1 5000 speakers, the difference is noticeable. Also a discrete sound card hogs less system resources. And not to mention Creative SB has a nifty gimmick which restores some effects lost due to music compression (Which helps 128/160kbit mp3s and also sounds in movies to sound better... \granted not all the time and sometimes it just screws up, but 9 in 10 cases it really helps)
Integrated generally gets owned by dedicated. Though some high end integrated ones can sometimes beat the low-few mid-range dedicated cards. Anyway, that is a high end dedicated so yes the sound blaster bombs the realtek.