I've had ReSound unit for about five years now. I bought them from a local audiologist who did a very thorough exam process. While they improve everyday life, I don't find they are very good for music. Things just don't sound natural (as I remember them).
Imaging, soundstaging.... just aren't there like I remember. I can only assume that due to the internal hocus pocus that is being done with phasing and such to make speech more ineligible, it is at a cost of messing up other things.
As a lot have stated, above 2K, things go south with my hearing. One issue I had was when I play piano, there was one note that would cause the units to feedback. Never had it happen in everyday life, but when I play it does. Audiologist explanation was, the ear canal can change the shape of the frequency response of the system (makes sense since the tests are done with headphones, but that in itself is a flaw).
The one thing that I wish manufacturers would do is make an option for audio minded people to have more that a 3 band graphic equalizer on them. I wish I had more control like a parametric so I could tune or shape the response to my liking, or should I say what I think sounds natural.
I tried a newer improved model a couple of years ago, but I couldn't justify $5,000 for such little improvement. I'm going to do more investigating into some of the brands that were mentioned in the thread to see if I can find something better. Resound is suppose to be a top of the end brand, but no one mentioned it.
One final thought which makes me think its my aids, I can listen to music with a set o JBL ear buds or AKG headphones and music sounds great. Don't notic the mid and high frequency loss, which further makes me believe the aids are not meant for music. Even then, speech ineligibility in a noisy environment is hit or miss. It is better than not having them, but far from perfect.