I understand your analogy between music note frequencies and B&W photography, but the part about being a painter and having steps of gray I don't know how to apply that to photography. Photography went down a separate path from painting 80-100 years ago.
I've read lots of things about the zone system too, but it's not something I practice; I don't use a spotmeter to check the levels in a scene, etc...
Things are made distinct by the total lighting setup rather than the reflectance of individual objects, and of course how colors are rendered by the B&W sensitivity. If you need more distinction between objects of medium brightness, you can use contrast to do that, and can reduce or increase scene contrast in the highlights or shadows so contrast is consistent through the range. Use a reflector or flash to boost the shadows, and a light diffuser to tame highlights.
If it's something you can't control the light in, like an outdoor landscape, weather, film choice and time of day choice are important. For example, when photographing rough granite (like the rockland breakwater) that has lots of similar tones and I want differentiation, I can shoot when the light is low and surface character creates more shadows. The low light angle emphasising the surface creates differentiation. Similarly, shooting rock when wet increases material differentiation.
I also use different film and or developer for different tone needs, in much the way you wouldn't be likely to use a harpsichord sound for low bass rhythm. TMY2 does a good job for film where I need to cover a wide range of lighting in a scene as it has a big "scale" it can handle. Pyrocat HD does a nice job with midtone and darker differentiation. PMK does a good compensating job for me where highlight detail is important and the rest of the scene has normal natural differention. For scenes where the range of lighting in a scene is narrower, I think fomapan 100 in pyrocat-hd does a good job.
In addition to the film choice based on sensitivity, filters do well. Skin texture for example can have different tone differention based on filter choice. red/orange to reduce blemishes, fomapan100/txp to increase freckles, etc...