I might well be wrong, but I don't think that bigger strings will get you what you want. Out of curiosity, what kind/brand of guitar is it?
Bigger strings will give you more tension, therefore more output, more volume, and depending what kind of strings they are you will change the tone a bit. But definition, or lack of, is due (I believe) to the guitar itself, the bracings, the materials, etc.... If you put bigger strings on, let say, your 6th and 5th strings, these strings are maybe going to be louder but you are not going to increase the bass response of the instrument.... theyre gonna be louder whatever notes you play on them
As I said, I might be wrong, but thats from what I have seen and heard so far...