The proton metal and the abyss are 2 totally different regulators. They are both constructed from metal. I'm surprised to hear you are getting a dry mouth from your abyss. Like I said earlier, most people are really pleased about the moister breathing that generally comes with a metal second stage. This is even why some companies put metal fins, tabs, etc. to achieve the moist breathing.
Yao,
Sounds like you are converting a the 2nd stage into an octo. Their are only three pieces you can buy to get as close to the all yellow second stage. Hose, little cover plug for the opening opposite the hose, and a yellow cover plate for the octo. All should be relatively inexpensive. As for detuning, I would suggest you have a qualified tech, do it. It's not complicated but you do want to make sure it's working properly should you have to use it.
All the best,