Accessing the service menu of the TV enables you to set hundreds of advanced settings. This page tries to list the interesting options that may worth changing. Be aware though, making changes in the menu may void the warranty (and/or make your TV inoperable). In addition, according to some people the TV is logging the changes made in the service menu.
When the TV is off, hit INFO-MENU-MUTE-POWER keys in this order. The TV turns on and you see a large menu structure. The service menu has a protected 'advanced' submenu. Press the 0 button four times on advanced to enter the hidden menu. Before touching any setting, please note the original value. The menu settings are listed (with their default values?) in the Service Manuals.
Enable serial console
Change setting for your RS232C interface to "debug" ( Control -> Sub Option -> RS-232 Jack -> [ Debug | UART | Logic ] ). More info is available on the Enable_Serial_Console_on_non_CI+_Devices page.
Configure sound delays
To eliminate the echo between the TV speakers and the external amp speakers, choose Control->SOUND, Change Auxout Delay Normal to the same value as Speaker Delay Normal (100). This can also be changed (in real time) to to find the perfect audio/video sync.