As for the AUX input, your GS350 should have an aux input in the center console storage area like pcdg said.
An Aux input is okay, but in this class of car, iPod integration should at least be a factory option. The Aux won't allow you to charge or directly control your iPod, so that's a drawback. There are, however, some awesome integration kits for the GS, so that's not really a problem having cassette, CD, and iPod capability. . .