I have a 1993 Toyota Corolla, and I am installing a new sound system. The Car Fit guide at Best Buy tells me that I need 6 1/2" speakers for the trunk, which will fit the two outside holes in the the top of the trunk, but there are two larger holes as well. I don't know what they are for, and I'd like to be able to fit larger speakers in there. Anybody know what they're for?