nothing like sticking a square peg into a round hole.
What manual did you read that it said 6"? was it an offical online user's manual?
Online User Manuals can be found here:
Owner's Manual
Here is a diagram from the service manual, that isn't on any online database that I've come across:
**Edit: no speaker size was shown.**
Sorry to say, but I think you need to exchange your speakers for smaller ones.