Kind of late here but I have some new info. We have a man with two Cochlear Implants who wanted to use our hearing assist system. I gave him a receiver and a neck loop, and he said he could not understand what he was hearing. Our system was old (About 25 years) but seemed to work OK. Perhaps a bit noisy, and you might need to position the receiver a bit for the best signal but it worked with plenty of volume. After talking with the people at Listen technology I learned that volume is only part of the solution. You and I can hear part of a word and our mind will fill in the rest. With impaired hearing this is harder. They need volume AND clarity. We replaced our transmitter and a few receivers with new from Listen. Same FM frequency and channel. The guy came up to me after the service and held up the receiver and said I CAN HEAR. I understood every word. I am keeping this receiver.
I tried our booth cans on a new receiver and it sounds just like the cans on the board.
BTW I am crazy cheep so we bought it all on Ebay.
BBTW I put a little delay on the system so those with some hearing get the same sound from there earphone that they get from the speakers. I did this after one guy complained of a echo.
Given this info, I don't think I would use anything related to smart phone or blue tooth.