The tC has two 6.3" speakers in the front doors, and two 5.6" speakers in the rear, BUT everyone who has changed the speakers has done 6.5's all around? Is that the best way to go?

 

most people put the largest speakers possible in the locations as long as you have the room. the rears have no depth issue so any 6.5" speaker will fit. as for the fronts you have to be careful with the window not to get a really deep 6.5" speaker.

 

in the front you have 3.3" of mounting depth......if you make speaker bracket/spacer from 3/4" MDF then you'll have just over 4" of depth which will be enough for almaost all 6.5" speakers.....