6inch or 6x9's

I'm curious as to weather on not to replace my current 6x9's (VDO QM6920) for some 6inch rear fill speakers. Because my new (2nd hand) car is a small hatchback. I was wondering if i'll get a lot of bass cancelation with running my subs as well as 6x9's. I'm also looking for a lot better overall sound. Not looking to have a car you can hear everywhere. I preferring the listening to be good for me... not the others outside the car like some ppl like to do with there setups.

My setup will be as follows - JVC KD-SX985 - VDO HPC 1700 – 6 ½” components running from Cadence Q4000 - VDO QM6920 running from headunit - Pioneer TS-W1001C running from Cadence Z1000 This hasn't been installed yet. But i was really looking into changing those 6x9's for a set of JBL GTO635.