Adding more speakers

[mitch27c]

I have a car with 4 speakers, 2 tweeters, and 2 subs, I want to add two more 6x9 speakers to the trunk, is there any way I could do this without buying another amp? Could I just splice them to the rear deck speaker wires?

 

[americanaudiophile]

You need to connect the 6x9s to an amp that gets a full range signal. The sub amps only get bass. If you have an amp that drives a passive crossover before going to the tweeters then that one could also drive the 16x9 if you connect them before the crossover. If you have separate amps for the mids and highs then you can't use those for the 16x9s.
Might not sound better anyway. More speakers can just muck up the sound especially is you don't have a way to balance them.