With Full Keyboard Access set to "Text boxes and lists only" in System Preferences, press<br>
<kbd>tab</kbd> <kbd>tab</kbd>, then the list is in focus and you can use the up/down arrows to navigate.
(even if the focus is not visible at first, which seems wrong)

With Full Keyboard Access set to "All controls",
<kbd>tab</kbd> through to "Songs", then "Library", then <kbd>tab</kbd> twice more and use the up/down arrows to navigate the list.