I'm no expert on music so I'm not sure what it's called but it seems like the opening screen song is remixed in the game. I mean it sounds like the beat is the same but has different instruments or something.
Original "Place I'lL Return To Someday/Place To Call home" you hear when starting up FFIX:
YouTube - Final Fantasy IX Music - A Place to Call Home
Then "Oeilvert" which you hear..iN Oeilvert:
YouTube - Final Fantasy IX Music - Oeilvert
"Ipsen's Heritage" from ipsen's Castle:
YouTube - Final Fantasy IX Music - Ipsen's Heritage
"Four Mirrors" played during the plan of attack on the Four Shrines.
YouTube - Final Fantasy IX Music - The Four Medallions
"Terra":
YouTube - Final Fantasy IX Music - Terra
Anyway, which is your personal favorite? Mine is the Ipsen version.