^^^ Before I had the AutoPhone mode enabled, I could not hear anything from my headset either, like what you found out for yourself with your husband’s headset. After I have the AutoPhone mode enabled, I would hear the phone mode chimed in when I put the headset on over the HAs. So it is the AutoPhone mode that allows me to use my headset with the OPN. The AutoPhone mode, when enabled, detects the magnet on the speaker of the headset when you put it on your OPN, and the AutoPhone feature then turns on the phone mode in the OPN (not your audi’s phone program, but the built-in phone mode). Although some people don’t think there’s a tcoil inside the OPN, I’ve seen some literature showing evidence that the OPN has a tcoil in it. I believe the phone mode (enabled by AutoPhone and applying the headset over the OPN) allows the tcoil to pick up sound in the form of the induced magnetic field generated by the speaker of the headset. That is how you can now hear the sound from the headset clearly, when AutoPhone enables the phone mode for you.
If you have a landline phone, and you put the handset on your ear, you’ll probably hear the phone chime as well when the handset’s speaker’s magnet activates the OPN’s phone mode.
When using the cell phone by itself instead of using the headset, at least on my Samsung Note 4, and probably on your Samsung S6 as well, I don’t think the cell phone activates the OPN’s tcoil. I don’t know why, but I’m guessing because these cell phone don’t have a big enough magnet on their speaker to activate the OPN phone mode. But I can still hear the sound OK from my cell phone. I’m guessing that in this case, it’s the OPN’s mics that pick up the sound, not the OPN’s telecoil.
My headset is a wireless Bluetooth Plantronics Focus. It’s paired with my Samsung Note 4. I use it for phone calls, but I also use it to listen to music from my phone (or laptop which also has Bluetooth connection). It also comes with a USB dongle to connect to laptops that don’t have Bluetooth as well. It produces great sound and deep bass also very suitable for music listening. But, I can also just hookup the TV Streamer to any music source for music listening without any headset or headphones, but via direct streaming as you already know. However, the TV Streamer is pretty clunky with all the wirings so it’s not very portable. For portability, I just use my Bluetooth headset.