The solipsist question here is, in what way can we really talk about anyone else's inner sensory experience and be confident that our experience is the same? What if (to take a trivial case), the color I call "green", if you could see through my eyes, you would call "purple"?

I think it has to do with information type. Sounds are basically one-dimensional, which means that all you need is a quick Fourier transform to de-convolute the individual components. Add in two receivers for spatial placement and you're set.

Sight just has a lot more information. There's color, contrast, movement, and spatial relationships, and every object constantly reflects or emits light, while only a few objects reflect or emit sound. Hence, a 2D visual field with two receivers for 3D placement.