Didn't know people were posting requests here, only just found out. The audio tool is outdated, yes. Best to look for someone else's hunting horn sound replacement and copy what they did.
Each model has different bone name numbers (under vertex groups), so when you copy one mesh to another model, you have to rename the bone numbers. I think there's a way to automate this but I haven't tried it yet. Possibly using Asterisk's tools:
You can only have one armature. You should delete the one you don't want, and then you need to update the armature modifier to point to the armature you want to use. It'll be red in the modifier list until you correct it. Then you should be able to export it.
As for tutorials, there are a ton here: