I have the Harmony One remote. Remodeling my HT stuff. I am putting all of my gear behind the wall out of sight. Will I still be able to use the Harmony One when all of my gear is hidden behind the wall?

You will need an IR repeater system. I use the Harmony One to control my HT and the rear mounted projector is controled using an IR repeater. It works great. The One is the first universal remote that has worked flawlessly with all my gear. It is now a one button start-up and shut-down process.