Sad that you're having problems with your board
I've owned/used an ep45-ud3p for several months now, and it works like a dream. realtek audio, ethernet, and all).
Out of curiousity, which OS are you running? I'm looking up the board just now to figure out which realtek chipset it uses... ahh... 889a audio, and an 8111dl for the lan. You definitely shouldn't be having problems with either... my board uses an 8111c for the lan, but I think the difference on those is simply a minor revision, not a major hardware changeup... final opinion is 'not sure on the network'.
Back to the real problem though, is that Gigabyte isn't coming through for you on the support, which is sad
I've never had to interact with them, so I can't say whether this is normal or not. However, I've heard many horror stories about Asus... but the real truth of the matter is that it's human nature to complain when they get a cruddy deal/situation... they're not so loud when things are going well... so you hear the bad, but don't always hear the good.
For the record, I'm using win7, and the drivers that come with, do a nice job with the audio. It sounds good, and I don't have lockup issues, etc, that you're describing. I'd suggest you've got a problem board, and not necessarily something wrong with the audio specifically. I was a little hesitant myself to use the onboard audio on this board, but I finally decided to simply try it out, compared to my m-audio revolution 7.1, which has a 'pretty good sound to it'. I am not displeased. For the record, I use a set of Klipsch pro-media 2.1's for playback, so if it were putting out crappy audio, I ought to be hearing it. It's not all that and a bag of chips, but it's a fair sight better than any other onboard solution I've tried to use.
Have you checked the gigabyte tech forums? They're actually not on the GB website.. they're here.. http://forums.tweaktown.com/f69/
Don't ask me why, cause I dunno