I'd try contacting Twist Dynamics and ask them if you can just purchase the rear bar that mounts to the roll hoops. Otherwise any local metal shop or maybe even an exhaust shop should be able to bend some tubing to fit and with a little welding, add some threaded blocks for mounting.
As someone who is literally dealing with this (with my Twist Dynamics Gull Wing), You may not have enough depth between the bar and the wing to accommodate a sound bar.
I'm trying to offset mount a bar to the top and then mount the speakers. Pics incoming once I'm done...
At one point, I had a set of 6.5" Wakeboard speakers (https://smile.amazon.com/gp/product/B008DJT5QK/) mounted to the rear crossbar of my TD Canvas Top, but I never wired them up as I purchased a set of Roll Hoop speaker enclosures which I've been using for several years.