I've now been using a new pair of Widex Moment 440 hearing aids (behind the ear) for about a month, and have been very happy with them. Using the aid's Music mode (vs speech) to restore the high frequencies I had been missing made a huge impact on being able to hear detail from musical instruments, such as the timbre of piano sound.
I learned some things in the process. These units can be ordered with standard receivers at the end of the wire (the component in the ear canal) or with "power" receivers. I tried both. The standard receivers do their job well, preserving the transparency of the music without introducing any sound artifacts that I could detect. However, the power receivers somehow made the musical presence sound constrained, like being in a narrow chamber, so I stuck with the standard receivers.
I also tried custom ear molds, vs. the neoprene ear cups that the aids are supplied with. Again, they seem to do something to the sound that I didn't like on my first impression, I may come back to these later.
The specified frequency response of these aids is from 100 Hz up to about 9 KHz. I was pleased that wearing these units did not impair my hearing's natural low-frequency response (from double-bass instruments for example).
I was also gratified that the standard ear cups work great with my Stax headphones. This is a big deal because placing any object close to the ears ordinarily increases the probability of acoustic feedback, so compatibility with headphones is asking a lot of any hearing aid brand. Fortunately, I'm able to prevent feedback by inserting the ear cup/receivers deep into the ear canal, which I learned to do with practice.
The Widex smartphone app has some customization features besides choosing modes and providing phone compatibility that I'll want to play with some more. I also bought their Sound Assist external microphone accessory, which really helps with speech intelligibility in a noisy restaurant setting.
Thanks again for everyone's experiences and suggestions!
Oliver