Brendor found that 0xC6DD4 is the byte that determines the Intro movie music (default is 0x1), and from that I was able to find a few more hardcoded songs:
0xC6434 - Title screen music (when the intro movie is skipped), default is 0x43
0xC5C9C - Title screen music (when intro is not skipped), default is 0x2
0xC4A0C - Prologue “Long ago…” intro music, default is 0x3
0x837B8 - Game Over, default is 0x3E
0x83628 - Unit died, default is 0x3F