This is an AMAZING mod!
As for myself, I was sold the minute I heard those glorious cave steps. Same with my brother, and now he's off to try the mod on his own computer with his 7.1 surround sound headsets. Point is, awesome doesn't even describe how good this mod is. It's hard now to think of Minecraft without these sounds. Man, why hasn't Mojang offered to add this in as a permanent feature?! Great job dude!
Here's my attempt at driving some more traffic towards this. Without a doubt, EVERYONE needs to try Sound Physics for themselves.