Is the AUX plug for input or output?  I have a non-ipod MP3 player - is that what it was intended for, using a male-male plug?  Or is it for passenger to use headphones?

Haven't acquired the vehicle yet - full of Q's that are probably in the manual.

I use the auxiliary jack for my satellite radio and it sounds great! On my first gen xb I just used the fm out to play the satellite over the radio and the sound quality was adequate at best. but with the new 2 gen xb I like having it wired right into the sound system and it is much better. The satellite and i-pod both sound really great. Kudos to scion for the improved sound system. Yes you can use a male / male cable to wire your non-i pod mp3 player. When I test drove my scion I wired my i-pod in that way to check the sound system "was not aware the ipod cable was in the glove box" I played Powerman 5000 "When Worlds Collide" and it sounded good ha ha. So I think your mp3 will sound good with the auxiliary jack. Another good tune for doing a sound check is "Nonpoint" (Bullet With A Name On It.) Good luck with your new scion when you get it.

Mine only came with the ipod cable.  I had to buy my own Aux male/male cable, and a 3.5mm>2.5mm adapter to work on my MP3 phone.  But it works.