Hey mate, nice choice on workin on an XG! I sold mine about a year ago to my brother. We put on a set of extractors, 2 1/2 inch exhaust, 3 inch pod filter (took out air box an fit it straight on to the rubber hose) new dizzy and plugs, and she ran a 15.7 at the drags. It only cost about $450 to lower, I put on a set of 17's set me back about $1300. There's not to much you can't do. Hard cover, XH bumper on the rear, color code all the bumpers. And yes 6 inch speakers fit perfectly in to the doors, if you can take the door trims off, you can see the gap you've got in the door to work with.
Feel free to ask anything you want mate!!