Back when Mega Man Zero/ZX Legacy Collection was releasing, Capcom offered Reploid Remixes DLC. This DLC was a preorder exclusive however, and were not available separately.
Now however, Capcom has made the DLC now accessible to everyone for free PlayStation 4, Nintendo Switch and PC. Xbox Should be coming soon as well.
The dlc “includes six alternative in-game background music tracks, as well as four specially arranged songs by series veteran composers available exclusively in the Music Player.”