Man.. I know its a little more work for you,like a couple hours.worth..But Id recommend sealing off those 6x9s,like building a cap for them to seal them up from the bass response/air movement that the sub is going to create.They will last longer and perform as they should if sealed off.The air movement from the sub is going to make those 6x9s move more out of norm/maybe too much and could damage them.I ruined a nice pair of JBLs that way in a Maxima with a dual 10" set up.I just bought some cheap 6x9 boxes and cut the face out and placed L brackets to secure to the deck and sealed with silicone.Went through 2 sets of 6x9s before I figured out what the hell was gong on..LOL That was back in the early 90s.Just something to think about from my experience,as I hate to see you possibly ruin your 6x9s, and excessive movement/cancellations/sound performance issues from the sub woofers response/movement /excessive air movement.They will perform/sound ALOT better sealed off as well,but the main thing, is to protect them, is from what I have experienced.