Actually, the tracks taken from X3 are strictly used when traveling. The tracks include Drums of the Goner (previously X3's Getsu Fune sector's theme), Yet to be discovered (previously X3R's Home of Light sector theme), Orbital Surfer + Aurora (previously X2-X3R's menu theme), Taming Stars, Tranquil Light.
The rest are indeed triggered in populated zones. Those tracks originate from X-Rebirth, Rebirth Home of Light DLC, and Rebirth Teladi Outpost DLC.
