I would add tweeters upfront. Having them in the back only will sound dull and boring upfront and you will be missing a lot of detail in the music up front. Tweets are cheep and easy to incorporate up front. What brand of mid/woofer do you have? See if that company offers tweeters. You could simply run wires off the mid/woofers to inline crossovers to the tweeters and call it a day.If i were to put midrange woofers in my front doors, and then coax 6.5s in my rear deck, would the tweets on the coaxials make up for the lack of tweets with the midranges up front, or is it recommended to add tweeters w the mids?