No audio, no mic

I have lost all audio function on my late 2007 MBP 15" Duo 2.53 GHz including the microphone and startup chime. I have tried every online fix and reset (PRAM),(SMC) I have restored the system 3 times OSX 10.5.8 and toothpick probe etc.....I was using the computer with external speakers for years with zero issues. Shut it down at night as usual and then next morning all sound was just gone. Here is the weirdest part. In audio midi setup my MBP says internal stereo output is not supported but I can route my MBP through firewire to a digital i/o box that has no sound card. I route to the external firewire device and all sound is restored through firewire i/o device headphone output! WHAT? That means my MBP is still putting out sound does it not? I am using this workaround for now but I would greatly appreciate any advice. I am known to be somewhat tech savvy but this one has me gobsmacked.