you mean 6x9's?
if so, dont mount 6x9s in parcel shelf.
1. whats the point in upgrading the sound quality in the boot (subs are put in boot because there isnt really anywere else you can put them and also the soundwave they give out is not as directional (i do belive but im willing to be corrected if wrong))
2. look at the speekers in the door, they are mounted onto metal for a reason, so that they dont bounce around ect. parcel shelf isnt strong enough to give it a good solid positioning
3. 6x9s dont give as good sound quality as normal component speekers.
if your going to mount speekers on the parcel shelf buy a stelth shelf