Hi,
I would suggest Dension Gateway. That's what i use in my IS250. You can take a look here:
http://car-solutions.com/en/Dension-Gateway-300-for-Lexus.php - that's where i've bought it from.
This gateway allows to control and browse your iPod and USB memory. Installation is very easy, you can do it even yourself, if interested - let me know, i'll tell how.
Minus - you will loose your CD-changer. Though you can get a CD router and in this case CD-changer will also work. But i have not bought this router, i'm just listening to ipod.
hope this helps, cheers.