Since you have both, you have the "lux" amp which is what the Denali should have (Denalis, Escalades, etc came with lux). In order for direct plug and play, the 2006 Denali needs to have the "lux" amp as well which it should have.
I was talking to the local GMC parts dealer and he said the issue will be that the wiring harness is different for the navigation so that would need to be replaced.....he made it sound like that would be a fairly big undertaking.....do you concur that the wiring harnesses would not match?
You may need to tap into the VSS wire to feed it to the NAV unit, but I am 99% sure that the harnesses are the same, and it's pretty much plug and play. You will need to have it reprogrammed for the new vehicle at the dealer though.
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