There is no "THE" C-Media. Their 8738 are PCI audio chips, the benefit being that they have at least some brain of their own, producing not too much CPU load. However they do use quite an amount of PCI bandwidth, which doesn't make everyone happy.
"Chipset audio plus codec" solutions, using C-Media 973x or Realtek ALC650 for six channels, are off the PCI bus, on the fast chipset internal bus. With KT333 and 8233/A/C or 8235 south bridges, the chipset integrated audio engine also isn't as brainless and CPU driven as public perception suggests.
Analog audio in/out quality however is ABSOLUTELY NOTHING to do with that choice. This is all about how much care has been taken during mainboard design. It's easier with separated codecs on an AC97 bus, since they can be placed in an isolated area away from all the high speed busses and in close proximity to the audio connectors, while a PCI audio chip always has to connect at least to the PCI bus obviously.
regards, Peter