Modifying speech in audiobooks to compensate for hearing impairment

I record my purchased Audible audiobooks so that I can modify speech to make them more intelligible. Slowing down narration works well for male narrators but not for female narrators.

I have tried changing pitch to make female narrators sound like male narrators. However, this does not not solve the problem. I only understand about 80% of the female narrator’s speech.

I am using an external sound card on a Mac. I play the audiobooks on an iPhone and make the connection between the iPhone and the sound card using a high quality bluetooth receiver. (I use this method as it avoids impedance mismatch issues.) The setup seems to produce clean audio. But I am not sure, as my hearing pretty well cuts off at about 4000 Hz.

Can anyone suggest a technique for solving this problem? I am reasonably familiar with Audacity, so I don’t mind a multi-step procedure.

I look forward to hearing from you. Thank you!

If it’s a sharp cut-off at 4000Hz that could be a limitation imposed by your computer, rather than your hearing, i.e. an 8000Hz sampling-rate bottle-neck somewhere, as commonly used in telephony.
[ I don’t speak Mac, so can’t tell where this bottleneck could exist on a Mac] .

If you’ve already tried Audacity pitch-shifting,
the only Audacity thing remaining is to apply an extreme treble-boost equalization to try to compensate for high-frequency hearing loss.
Bear in mind that ∞ x 0 = 0:
if there is no hearing whatsoever at some frequency, amplifying it will not make it audible.