I have an P8Z68-V PRO/GEN3 with onboard ALC892.
If you plan on using a receiver and using the optical out then onboard will work great. Ive used higher end sound cards from Creative for 10+ years and I cant tell a difference in Analog out (creative) vs digital out (mobos). But I can tell a difference in analog out (creative) vs analog out (mobos). The mobos Ive used over the last 10+ years all have inferior analog output compared to dedicated sound cards
One reason for switching is that I wanted to get away from a PCI card. I have one PCI slot used, and the other is very close to a very hot video card. I had a lot of driver problems with the Xfi and XP . I'm reading that the hacked PAX drivers are good in Win 7. After reading some yesterday, I might just install the elite pro and try the Pax drivers
Thats good reasons for switching cards. If you dont have any luck with those win7 drivers and dont plan on using the optical out on the mobo, Look into the Asus Xonar line.
http://ixbtlabs.com/articles3/multimedia/asus-d2.html
"Both cards demonstrate the highest audio quality, it's very difficult to choose the best card. We haven't heard any differences in some test fragments. Others demonstrated a hardly noticeable difference in playback personality. The X-Fi demonstrates a tad more distinct attack, while the Xonar D2 provides a tad wider stereo base. I repeat, the differences are so measly that we had to switch between the devices many times to hear them. It's even more difficult to understand which card sounds closer to the original.
However, this situation is typical of modern High-End devices - it's very hard to hear the difference even with a high quality audio section. Manufacturers of popular devices have come close to reaching full potential of High-End converters. So you cannot expect a break-through in this field - the quality margin of audio components is disappearing. On the other hand, we can certainly recommend such cards as Xonar D2 and X-Fi Elite Pro for owners of high quality audio equipment, to say nothing of top active speakers."
This is what I was getting at in my first post. Sound cards are so close to each other that it's darn near impossible to hear any difference.. It really comes down to what features you need.
Gaming support (Dolby Digital Live, Dolby Headphone, EAX, cmss-3d)
Home Theater connectivity support like, 5.1 analog out
Headphone support (built in headphone amp, Dolby Headphone)
Audiophile support (op-amp swapping, Superior analog output, analog output connectivity options like RCA out)
Thats most of it but there is more.