Came across this on another board, there are apparently several different ways to access the menu.
One way says to hot the 'display' button and then alternate tapping between the top left and bottom left sides of the screen (about 4 times in a row)
The other way is to hold the INFO button and turn your headlight stalk all the way on/off 4+ times. This is the way that works on my 2008 IS-F, so YMMV.
One of these should work on the GS, LS, RX, etc as well.
I did this because I was hoping to find some settings to turn down the center speaker, but alas, I didn't. I did find a variety of other information though, and took a picture of every menu that had anything to say. This is also apparently the menu you want to get into if you are having bluetooth issues (with people not being able to hear you clearly)
Here goes:







Lexus hidden diagnostic screen (w/ navi system only)
Lexus hidden diagnostic screen (w/ navi system only)
Lexus hidden diagnostic screen (w/ navi system only)
Lexus hidden diagnostic screen (w/ navi system only)
Lexus hidden diagnostic screen (w/ navi system only)
Lexus hidden diagnostic screen (w/ navi system only)
Lexus hidden diagnostic screen (w/ navi system only)