In reference to your question as to why there’s no way just to send the sound direct to the brain; the top 40dB or so of your hearing occurs as the basilar membrane’s response is ‘tuned’ to the incoming signal. This means that your brain actively tunes (through afferent/efferent) nerve action the receiving surface of your ‘microphone’/cochlear many thousands of times a second.
This means that if you wanted to add a real microphone to the system, you’d have to cut into the cochlear nerve and match the reference afferent incoming signal across thousands of fibres, process for relevance and then let the brain respond with efferent tuning of your mic to raise the response of the mic level at a particular pitch while simultaneously re-sending the resultant signal back to the brain.
It’s possible (at the electronic level), but I’d like to see you do it real time, with negligible power, in a body concealable device. As for hacking into the cochlear nerve and connecting to it in a meaningful way without destroying the surrounding pathology, I’m not sure that would ever be feasible.
I’d say you’r a bit further out of your depth than you realise here.