- Find the Ambient folder in your League of Legends game folders-- my path was C:\Riot Games\League of Legends\RADS\projects\lol_air_client\releases\0.0.0.117\deploy\assets\sounds
- Rename the files with a .orig after the original name so you don't misplace it.
- Copy the music files you wish to play to this folder. You'll need to rename them to the exact name that corresponds to the music type--ie. ChmpSlct_BlindPick for the Blind Pick (Normal, non-draft) games; or ChmpSlct_DraftMode for Draft, etc.
- If anyone can figure out which of their provided tracks are the in-game music, please let me know-- that'd be awesome.
- I suggest you close and reopen the League client to ensure that the changes take effect.
(all music belongs to their respective artists)
Let me know how this works out.