| Two drivers that have very good SQ and will loosen everything in your car are the OZ Matrix Elite and the Image Dynamics IDmax. They don't require a ton of power either as 600-800 is perfect to get them very loud. Both work excellent in sealed and ported enclosure's and both are right at the top of the SQ ladder.
If you're already feeding your AVI's 500rms or more then I feel switching to one of these two drivers would yield more output with similar power with just as much SQ ability.
What amp are you currently using on your SLS300's? | 
