If you care about the quality of you audio, yes it very much is worth it.
Just do your self a favor and avoid any Creative products....
For an excellent quality value card, I would highly recommend either the ASUS Xonar Dx (PCIe) or Xonar D1 (PCI).
Both offer exceptional sound quality, especially considering the price.
Well, I have tried the HT Omega Striker, and I can tell you it deliver. The price is nice and the sound quality is awesome. 10 bands equalizer included for the sound that you research. This thing is ideal for music, videos and gaming. If I remember well, EAX is also supported. A nice 7.1 dolby compatible soundcard.
Onboard sound is actually pretty good with X58 motherboards... The question is, is the difference between very good and great worth $100?
It will never be able to match a DSP emulating your sound. Sound cards are as important than video cards. If you can spend useless money on a LGA1366 board, you can spend 80$ on a high end dolby sound card for making your PC the perfect HTPC.
The difference in quality isn't even close. You can adjust every bands of sound to get the sound you want. Onboard sound don't do that.
I would just try the onboard first when you get it, if you like it, chalk it up as $$ saved and be happy. If it's not to your liking, get an add on card. But I know on my board, it is supposed to be 7.1 hi def sound. Don't ask me how true that is, but seems fine for what I do.
Thanks for the feedback. I've decided to save a few bucks and go with the onboard sound. As has been suggested twice, I can always upgrade later if not satisfied. Also, thanks for the alternatives to Creative. I have always used Creative's cards in the past and have had no trouble, but its been 5 - 6 years since I've purchased one.