There is physically enough room to mount 6X9's in the rear of the tC. However, you will have to fabricate a baffle board or enclosure behind the panel. Then there is the issue of the grill. The sound would be blocked and muffled by the small hole in the stock grill. The rear speakers on the tC really don't sound that great in the first place due to poor coupling and no real baffle to seperate the front and rear soundwaves. In order to mod it for 6X9's, you would have to do some extensive work to make it sound right.