How hard would it be to make this modification to my SWR WM 15? I want a dial that will let me control the volume of my horn separately from the 15. I'd like to keep the horn one, but tone it down a little. What parts would I need? Also, how much would I benefit by replacing the horn with a better one? Maybe that would make it less harsh and I wouldn't need the dial. Anyone have a recommendation for a replacement horn?