I created https://news.ycombinator.com/item?id=49469365 to see how many people perceive things this way.

It is quite possible that this is drawing a line, as you say, between hyperphantashia and regular phantasia, though I'm not yet willing to give up on the idea that we are just giving subjective names to the same phenomenon.

To wit, when I "hear" things with my "mind's ear" I can "hear" them very well in all the layers and components, I can "hear" drums and guitar and bass and voice, etc., but they are very clearly in my head -- they do not have a location in real space the way that real sounds do; I can't "hear" a sound so loud that it makes me cringe or so quiet that I have to strain to hear it.