I have an Asus MB though not the same model and have always had problems with sound after an install, there is what works for me, I simply replace the AppleAzaliaAudio.kext with the one from tiger, or search online for an older ver. than what is included with leopard. Now I am not saying that this will fix you problem because your issues could be more than that but this is what works for.

They are on-line tutorials on how to replace kexts, let me know how it works out.