Lexus use Navtech map information which they combine with other info so a normal Navtech disc will not work. Aisin and Denso make the sat nav system and only Toyota/Lexus discs work.
The JDM nav unit is different from the European versions. People have tried putting a UK disk into Altezza, Aristo, Soarer and Harrier and it doesn't work - so there is no reason to think it will work in the Celsior.