as seen in the link above this Vais unit allows you to have two additional audio inputs into your OEM sc430 head unit. It will display "AUX" on your screen. This unit is plug and play and will not require you to splice any of your cables. It is a great way to add audio from your iphone and other devices.
Price is $100 shipped anywhere in the US. Vais I believe charges $150 for the new one. The unit has been lightly used..my 04 SC430 hit 15,000 miles last night.
I also have a WDTV that was hooked up to my NavTool, with the Navtool and the above listed Vais unit I was able to stream movies from this device:
I will let the WDTV go for $50 shipped anywhere in the US. The WDTV does not include the AC adapter, only the remote and actual WDTV unit. The adapters are pretty inexpensive online. Buy both and ill knock off $10.