OK, the 2005 3d is an easy upgrade
The OEM Plug is BR8ES, and the upgraded one is BR8EIX
But on the 2006 DI the OEM is ZFR4F-11, and NGK doesnt have the iridium upgrade option, but a website mentioned that ZFR5FIX-11 is the equivlent. However, its one degree colder.
Are these numbers...