[joshnerius]

> I personally know several musicians who have a deep understanding of music theory, but don't read music

"don't" or "can't" read music? I think this is a critical distinction. If the answer is the latter I would still argue that they cannot have a deep understanding of music theory, since a major component of music theory is generally accepted to involve understanding notation.

Edit: I can accept that there are many aspects to music theory that go beyond just notation, but I am skeptical of 'deep understanding'.