I just got P3D v4 and decided to setup VA for it since P3D's voice control is pretty pathetic. It wasn't as easy as setting up X-Plane or just about any other program so I thought I'd document what I found here since most of the discussions on the net were not really helpful. From what I could find things changed with v4 for many people.
It's been a few years since I worked with an MS flight sim since I went to X-Plane when MS bailed on FSX but I got P3D to fly a few aircraft that are not available in X-Plane. I started with FS5.1 and have tested every version since as well as doing panels and working with the internals.
First, I started getting the you have a Nahimic app warning which I had never seen. Turns out it's from my EVGA NU audio card which uses it for effects. I installed a replacement after my original failed and had not run VA with the EVGA card before. Fortunately, Gary's tip on turning on "Disable Acoustic Echo Cancellation" worked.
I created a profile with a couple of simple commands to switch views and set them to go to the window *Prepare3D* which is a regex for P3D's main window. Nothing worked. I include a text to speech readback so I know the command executed but P3D never saw it. After a lot of testing I found that the following needs to be done.
1. P3D runs as Administrator - I had to do this any because evidently there a plugins that require it. Who knows why but it is what it is until the authors figure it out.
2. I also had to run VA as administrator. I have never had to do this before for anything but I guess since P3D is run as admin so must VA.
After working with X-Plane and it's API I'd forgotten what a steaming mess of code MSFS was. It appears Lockheed is trying to clean it up and more power to them.
Hopefully this helps someone.