can you borrow some other speakers ? even some basic "home stereo" speakers to try.
You can see how i built the Hangers on the studio build thread.
start on page 5 in the middle of the page Steve's new Recording Studio from the start
You can cover them with reflective material if you want to retain the highs. I covered them with 3"703 and cloth and it works great.
these hangers would fit perfect in your ceiling and if you trap the corners with 4" of 703 and built a 24" deep trap on your back wall filled with the hangers that would make a Huge difference.
Hangers do tend to work better at High SPLs,
they are super quick and easy to build
You can hang them with rope , chain, heavy wire or plumbers tape.
steve