but he is also a very picky man who was a mechanical engineer so I feel like his expectations can be a little high sometimes for things to be perfect.

Approach this as an engineering problem. Engineering core principles start by defining: What problem are we trying to solve?

Further, good engineering is forming the right goal. If the goal is: "We want to be able to restore the hearing of a 70 year old man to that of an 18 year old one", the we should reject the premise. Technology simply doesn't exist yet that will do that. We need a less ambitious goal. Something like "How do we restore the ability of the 70 year old man to understand the spoken words of someone who he is seated in the same room with." Now THAT is probably doable, but it comes with tradeoffs.

One thing he has said was that they change how loud some things are compared to how they should be which I think he means they will make certain pitches louder than other pitches so something like setting spoon on glass plate will be loud but the sound of a low voiced man talking is quiet when normally the low voices are the only ones he can hear.

This is a consequence of what resources in the human are left to work with in our 70 year old man. A lifetime of mild and moderate hearing damage and general aging process means that not only are the high and low audio spectrum reduced, but also specific frequencies are missing because the nerves for those frequencies are damaged and none functional. Many hearing aids will shift the register of a sound into a range that it knows the hearing aid wearer can still hear. This is why pitches are shifted and sound strange. One person with extreme hearing loss may only be able to hear spoke word as though it were Sesame Streets high trill voice, but make no mistake, they would make out the words and be able to converse with the other person.

One solution that was a GAME CHANGER for us was an external microphone.

Most of the middle and high end hearing aid brands have one or support one. They go by different names but they're all the same:

• buddy mic
• companion mic
• partner mic

I had to find out about these myself looking for a solution like you were. No audiologists or hearing aid expert ever mentioned these to me and I have no idea why. These are small battery powered label mics that are paired directly to their hearing aids:

They're not crazy expensive (a couple hundred dollars). These can be clipped to the lapel or set on a nearby table near the other speaker and they do a MUCH better job of picking up sound compared to the built in mics inside the hearing aids. The one we have for my loved one works this way. When it is vertical (like on a lapel) it is a narrow focused mic so it only picks up the voice very near the speaker's mouth. This is great in a noisy room because it intentionally localizes the speech the person wants to year. When laid on its side it switches to omnidirectional picking up as much sound AROUND IT IN ALL DIRECTIONS. So if you're at a large table, you set it in the center and can hear everyone speaking around it. While there are better solutions, in a pinch you can also place the microphone near a TV or other audio source if you're with a group watching something on TV. This will let them hear it too and be a part of the shared experience.

If his hearing is so extreme he is not able to stay involved in conversations unless someone is yelling in his face, I STRONGLY encourage you to work with him to get some kind of solution in place. Advanced aging is an exercise in forced isolation. Your hearing falls away so you can no longer bring auditory input. Each of these isolates the person further. In the end you're just left alone with yourself. Fight against this for as long as possible.

My loved one told me about the isolation they felt without being able to participate in the conversations. This is how I learned about this. For my loved one, this brought them back to who they were before the hearing loss. It was a bit cumbersome to turn the mic on and off sometimes, and the battery lasted something like 8 or 10 hours, so recharging is a thing too. All of that trouble is so worth it though for them gaining their ability to connect again. She uses it all the time now completely on her own and has no shame in telling people that they have to use it with her. This has helped especially well when dealing with medical professionals which old people have a lot of. She takes the mic out of her purse before the doctor arrives, turns it on, and hands it to them asking them to put it on their lapel. She is FULLY ENGAGED in the conversation and after a minute or so you even forget she has hearing aids and there is a microphone on the doctor. Ever single doctor or medical professional we've had loved having this mic when working with her. She is clearly able to understand everything they say with it. When she was in the hospital the regular staff knew about the mic and would automatically ask her if she'd like them to use it for that session. It made their jobs easier and her experience a thousand times better. We've had to chase after doctors that forgot they had it on to get it back a couple of times.

One more thing, because this is wireless and you easily forget about it. Take the microphone off when you step away to go to the bathroom. :)