I recently did a DIY project like this for my 2001 Sienna.
I got a aux adapter for $40 and connected to the cd changer port and I dont have a CD changer. So you'd lose your CD changer if you want to install an AUX device. The aux device will give you rca inputs to which you can hook up any device like mp3, ipod etc.
Need to hook on my mp3 player but do not wish to go the FM way as that drastically reduces the sound quality. Too bad... my Toyota Corolla 2006; 6 CD changer doesn't have AUX inputs
Have come across several add-ons that create AUX input for the stereo system. Which is the one that a novice could connect based on the step by step instruction provided with the product... you know the DIY kind? I don't wanna pay $100 for the device and another $100 for installation!!