I couldn't get 6x9s to fit when I first started either. I ended up cutting the piece out and installing a custom one. The hole was physically too small for the speaker to fit. They changed the speaker size from 5x7 to 6x8 in 98 so maybe the hole size also changed? Another theory: maybe premium setups had 6x8s and the sh!tty tape decks came with 5x7s. There seem to be a few people who can't get 6x9s to fit.
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The Honkeytonk Monkey
Jewel Green 96se MTX