For example the GA-8PE667 Ultra 2 with that chipset has the Realtek ALC650. A description of the chip from a quickly searched website is as follows:
It is an 18-bit, full duplex AC'97 2.2 compatible stereo audio CODEC. It supports full surround sound 6.1 configuration with a maximum of 6 separate or discrete channels (Left, Right, Center, SL, SR and Sub). The ALC650 also supports an AC'97 2.2 compliant S/PDIF out function where there is a onboard connector for a S/PDIF Module (RCA Cable and Optical Cable).
That's pretty good for an integrated chip, and there's a fairly large segment of the population who would probably consider that to be adequate.
A typical PCI card like this will add an additional cost of $40-$50 dollars to the cost of your system. Is it superior to the onboard chip? IMHO, yes. But is it necessary for gaming? Perhaps not. That depends entirely on your ears ... what kind of quality of sound <i>you</i> want while gaming. It also depends on the speakers ... if you are using $10 Yamaha speakers that are two or three years old, then there's no point to adding a PCI card and wasting the IRQ's. But if you have decent quality speakers, like the idea of EAX 2.0, and prefer to have lower CPU utilization and memory usage levels than can be achieved with an on-board chip, and want better quality sound ... spend the money.
Personally, I've got a Hercules 6.1 sound card and breakout box that I picked up for a decent price. That's on one system, with good Klipsch speakers. On the other computer, cheap speakers, using the Creative CT-5880 integrated chip.
There's no doubt that the Herc card sound quality is far superior in every respect. But do I need it for games? That depends entirely on my personal taste. In this case ... yes, I prefer the sound off the Herc card and Klipsch speakers. But when using the other computer, I don't expect that much, and that's exactly what I get. Not much. But bright, tinny sound is better than no sound. Right?
Your choice. Whatever makes you satisfied, and pleases your senses ... that's the ticket.