Aficionado is an apt term to define the person within the context and it gives the emphasis on having the knowledge in a particular subject, and is often used in musical context and with music genres. Here is a very similar example to yours:
A music lover by age 3, Boyd listened to his Vienna-trained grandmother play Brahms on the piano. Then, with Princeton pal Geoff Muldaur, he became a teenage aficionado of blues and jazz records.
If someone is an aficionado of something, they like it and know a lot about it.
I happen to be an aficionado of the opera, and I love art museums.
...a jazz aficionado.
You could also use music aficionado in your last example:
He is well-read and his brother is a music aficionado.
I don't believe there is a specific term for songs or even music like well-read, at least not in common usage (Musical is too broad and not a good fit for your examples, and you've rightly eliminated it before). Well-listened comes to mind but it looks like it didn't become an established word and it is not defined in any dictionary, although I've found some examples with relevant usage. Here is an example from a credible source, Princeton Alumni Weekly, Princeton University:
There is no doubt that Steinberg has read extensively about music and listened extensively to music, making him both well read and well listened; in fact, it is unlikely that anyone in the field, past or present (and that includes the great Donald Francis Tovey, who is one of Steinberg's acknowledged role models as a critic and annotator), was, or is, better read or better listened.
You've mentioned that you already know well-versed and you are not looking for it; however it is well-worth of consideration as it is commonly used in musical context. Here is an example I've found, specifically used with "songs":
Krall also boasts an extensive knowledge of the great Tin Pan Alley standards of the twenties, thirties and forties, as well as being uncommonly well-versed in songs from the sixties onwards.