Ok, I grabbed a bunch of Snow Leopard kexts (build #A432) that could possibly have something to do with your headphones/speakers issue and posted them here:
http://rapidshare.com/files/27033667...Kexts.zip.html

I would start with replacing AppleHDA.kext, then the other audio kexts, then the lower level kexts.

I assume you know how to replace kexts, but in case you don't, use something like Kext Helper here:
http://cheetha.net/

I hope you partitioned your hard drive and have Leopard (10.5) installed as a back up OS X installation you can boot from.

Good Luck!