new honda owner wanting to make changes
 

Hi Im Josh and I just bought my first Honda Civic, a 2010 ex.
I really like the car, but am wanting to make a few changes, and I don't want to do anything that will void any part of my warranty.
One of the things I have been looking at doing is replacing the factory exhaust with a cat back. I don't want it to be too noisy and I want an improvement in fueleconomy and of course a lil boost in power. Of course a new intake is also on my list.
Last I would like to improve the tunes. I have the stock head unit (no navigation) I like the head well enough, but the speakers need more range. What speakers would anyone here recommend. Also I would like to add a sub without taking up any space (perhaps in the stock location). I'm not looking to thump the doors off the car, but I work in the music industry and after going to shows 5 nights a week for the last 2 years, i have become a bit of an audiophile, and like the feel of good solid bass, crisp highs, and full mids.
If an aftermarket radio ends up on my list, I want a navsystem, and i want it to look pretty stock.
Thank you all for any suggestions you have.