SB, that’s a lot of work, detail and tremendous amount of time for mounting a tv and sound bar. Maybe a sub it appears? Why not just suspend a p-ring centered where the sub cutout will go

To further complicate things, the electrical contractor did the low-volt rough in based on my wiring schedule so I wasn't onsite as much as usual to keep an eye on things.

Somewhere through the process, the contractor just sheet rocked over the wall and decided to also add a tremendous amount of blocking and backing material to make sure I had something to attach the TV to...

So I guess the short answer to your question is this was all just laid out onsite much like a retrofit job. I mocked up an image in Photoshop showing the approximate size and location of the TV for the client to sign off on before ordering the frame. Then I took a photo I had of the wall before sheetrock and taped it up with cut sheets for the Edge Frame, wall box and subwoofer and then started laying out the wall with blue tape.

Also made some cardboard templates of the wall box and sub to help with the layout.

In the end, had to cut out some blocking and backing material that the builder installed and then was able to drill up through all the blocking to run wires and conduit to the attic.