I actually installed an XM kit (antenna,modulator,splitter) from Toyota(made by Pioneer,Thailand) for the 2004 LS430,which costs $400+ from lexuspartsmall.
It is better than these Delphi implementations because it is not subject to FM modulation.
You will need to install the splitter connectors into your trunk (where the amplifier connections are) and install the XM box under the Lexus Link holder, aside from installing the antenna over your trunk and routing the wiring to the XM box.
The most difficult part of the install was uninstalling the trimmings and installing the rivets for the revised trim "box" for the XM box.
I used the savings I got to buy a 2-year "discounted" XM subscription.
By the way mention the XM promotion from Lexus and you get a free month's subscription and free activation. :P