I actually just found a list of every soundtrack you can listen to in game, and the list consists of:
Final Fantasy I
Final Fantasy II
Final Fantasy III
Final Fantasy IV
Final Fantasy V
Final Fantasy VI
Final Fantasy VII
Final Fantasy VIII
Final Fantasy IX
Final Fantasy X
Final Fantasy XI
Final Fantasy XI Rise of the Zilart Original Soundtrack
Final Fantasy XI Chains of Promathia Original Soundtrack
Final Fantasy XI Wings of the Goddess Original Soundtrack
Final Fantasy XI Original Soundtrack -PLUS-
Final Fantasy XII
Final Fantasy XIII Original Soundtrack
Before Meteor: Final Fantasy XIV Original Soundtrack
A Realm Reborn: Final Fantasy XIV Original Soundtrack
Final Fantasy Type-0 Original Soundtrack
Dissidia Final Fantasy Original Soundtrack
Dissidia 012 [duodecim] Final Fantasy Original Soundtrack
Final Fantasy XV Original Drive Music
Final Fantasy XV Afrojack
Justice Monsters Five Original Soundtrack
Kingsglaive Final Fantasy XV Original Soundtrack
All of the music not given to you by default is found at stores throughout your trip, so when you stop by a new shop make sure you check out the store and see if they are selling more soundtracks.
Source: http://www.novacrystallis.com/2016/09/heres-music-can-listen-final-fantasy-xvs-car/