Keep in mind that hearing aids, even the latest and greatest, are not suitable for arranger keyboard playing. Hearing aids are nothing more than an amplifier with a built in mic and speaker, both of which are very, very tiny. They are meant to improve your ability to hear sounds/frequencies that you are missing, during normal conversation - not musical instruments, electronic or acoustic.
When the hearing aid specialist adjusts your hearing aids, he or she is setting them by amplifying the frequencies that you have lost from various reasons, infections, trauma, etc... Therefore, some sounds coming from your keyboard will sound tinny or harsh. Now, that frequency is amplified by digitally selecting that frequency, and cranking up the volume. However, that tiny device that fits in your ear, which in most instances is a small balloon device fed by a tiny, clear tube, is blocking off the sounds you would normally hear, mainly bass and intermediate frequencies. If you have a hearing aid in both ears, you are missing a lot of wonderful sounds.
The solution is to wear a hearing aid in just one ear, the ear that you are having the most problems. They can determine which ear it is at the hearing aid center, but they want to make a huge amount of money by selling you two, claiming all sorts of stupid things such as loss of balance, etc..., none of which have any medical documentation to back these claims up with.
How do I know this? I purchased a pair of Bose hearing aids, which were relatively inexpensive in comparison to the highly advertised brands on TV. When I played with both aids in my ears, the highs and mid range sounds were just awful. However, when I removed one and only played with one in my right ear, which was the most damaged, everything sounds great. I was a first loaded of a 3-inch 50mm antiaircraft gun while in the US Navy. I stood back to back with another first loader, directly between the breech of both guns - no hearing protection and the blast was horrendous. When the guns fired, I was looking at the back of the gun, where the loading tray was situated and pulling out another round to be placed in the hopper. BOOM! You were instantly deaf for several hours. They didn't care back then, you wee 17 years old and expendable, and so was your hearing.
As we age naturally, men tend to lose their high frequency hearing ability, while on the other hand, women tend to lost their low frequency sounds. Now, maybe nature intended this to be. I cannot hear her when she is telling me what I did wrong for the past 61 years, and she cannot hear my replies.
Good luck,
Gary