· Can I use the Rio Car player in an audio competition?
The player's audio output circuitry is certainly of competition quality. And if your MP3s were created carefully and are of high quality, they can sound every bit as good as a CD.
However, most audio competitions don't accept MP3 players for the Sound Quality part of the competition. For example, the IASCA competitions require that the judges supply the CD itself. This might change in the future, but for now, you must use a CD player in most competitions.
Remember, though, that you can still use the Rio Car's line-level aux-in jacks for a CD player. This would let you use the player's 20-band fully parametric equalizer to adjust your sound. This might be helpful in a competition setting. You could, for example, create an EQ preset for each of the different stages of the competition.