Since you live in California consider having Factory Radio Service add an aux-in to your head unit: http://factoryradioservice.com/page.html?id=1

I got the most "deluxe" version of their aux-in on my LS radio last year for $85 not including shipping. They modified and shipped my radio back to me only one day after receiving it. The deluxe version has the 3.5 mm aux-in port on the back of the head unit, an on/off button on the front of the head unit and comes with a 6 foot 3.5mm cable. It works perfectly and provides absolutely perfect CD quality sound. I've since loaded most of my music to a micro SD card in my phone but mainly have been streaming Internet radio such as Pandora, Slacker and Tunein.

Here is a thread about it in the LS400 forum: https://www.clublexus.com/forums/ls4...000-ls400.html
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Edit: Sorry I later realized that you also have an SC430 for which there are a number of commercial aux-in products. Just buy a "plug and play" aux-in interface and forget about having anything custom built or installed.