Well, I don't give up easily. I reached out through the developer's support email and reached an incredibly helpful guy. Gábor Szántó. Gábor is the developer of Hearing Aid Pro and was quite willing to explain why the app was not designed to be used with wireless headphones.

As designed (originally) the app was using the microphone on a standard iPhone headset, which has a built-in microphone. As normally connected, this microphone is wired directly to the phone and offers a very fast connection for the sound to get to the phone to be processed. Audio engineers refer to this as "low latency". Regular people just realize the issue as "no echo" or "no lag".

He explained to me that if he allowed the bluetooth headphones to connect and use their microphones (as the app was designed) then there would be a lag while the headphones sent that sound to the phone for processing and another lag while the sound was sent back to the headphones to be played.

We continued our discussion over a few hours via email exchange. I honestly forget which of us suggested using the microphone on the iPhone itself do the capture of the surrounding audio, since it was on the phone already and would not have the lag time. Regardless, both of us were excited about this idea. So, forward with that plan. I offered to test the app since I had access to these headphones

In under an hour, Gábor sent me an email with a link to the first beta version of the app with this idea implemented. I was able to connect the app, but there were a few weird behaviors. We went on that way with me explaining issues, and Gábor tweaking his app. Within an afternoon we had a version of the app that worked pretty well with the TrekZ Titanium headphones.

I wore the headphones and used the app at a biology seminar that afternoon and was utterly amazed. I heard every word the speaker said that day. Even better I heard all of the questions asked, even the mumbled ones from the back of a large auditorium! I let Gábor know we were certainly on the right track!

Sadly, I had to return my borrowed headphones. This meant that testing was at a bit of a standstill. I reached out to the marketing team at AfterShokz and me the awesome Caleigh. After hearing my story she graciously offered to send a pair of headphones for me to use in testing. She also sent along a pair for Gábor, though I am still working out details on shipping to Hungary (it's challenging!). After a couple more slight revisions to the app it is pretty darned reliable with these bone conduction headphones.