You can try this: http://voodoohda.googlecode.com/file...ooHDA.kext.zip
It is the VoodooHDA.kext which is working great with my setup(I also have ALC883).
I've tested it using leopard 10.5.6-10.5.7-10.5.8 and snow leopard 10A432.
Just tell me if it works or not! :-)

About my system:
Motherboard: Supermicro H8DAE-2 with nVidia MCP55 Pro chipset which supports up to two Six-Core AMD Opteron 2000/8000 processors
Super Micro Computer, Inc. - Aplus Products | Motherboards | H8DAE-2
Processor: 1x Opteron 8214 (for the time being) :-)
Ram: 4 GB Samsung DDR2 667 Registered ECC Unbuffered
Graphics Card: Nvidia 9400 GT
I also have two SATA hard disks, 120 GB and 640GB , a Sony IDE DVD reader and an Optiarc DVD Recorder.