If you could explain to me what i would need or if the KVFM1 is compatible with my player, that would be great...

Are you sure you know what an FM modulator does? It does not add an FM tuner to your Rio Car player.

It's a way to connect a third-party line-level audio signal to a car's factory radio. It is compatible with the Rio Car player in the sense that it would take the Rio Car's line level outputs just fine. It turns that line-level audio signal into an FM radio frequency.

You asked if we could explain "what you would need", so here is what you would need:

1) A car radio with an FM antenna input.
2) Room in your car's dashboard for a second stereo.

Then you would connect the Rio Car to the KVFM1, connect the KVFM1 to the car radio, tune the car radio to a certain frequency (in the KVFM1's manual) and then press "play" on the Rio player.

But I do not recommend doing this unless you have absolutely no other alternative. It's better to remove the factory radio and install an amplifier to listen to the Rio Car player.