Well, the premium package comes with some 6x9 Bose subs on the rear deck (right below the rear window). I don't have the premium so I don't have the 6x9. Do a search on the forums about people removing the 6x9 and you'll know what I'm talking about. Yes, I'm talking about the coupe. I personally haven't seen these 6x9 but they are there from what other members are saying *shrugs*. Anyways, if you want to remove it, I don't think it will make much more bass but hey, every little helps Now, if you mount the some subs in the rear sides (maybe 6x9, only a few manufacturers make them), this will create a sealed enclosure (kinda). You will have to at least dynamat the rear side panals but at least it will make it sound like it is sealed. I haven't really done any of this and so this is just sort of in-the-air. I have to take a look and experiment and see what kind of sounds I will get by doing all this. You may be right that by removing the 6x9 will give you some more bass notes but from what I've done in the past by raising the back seat up, I get less "boomy" bass, albeit quiter. This is true for vented/ported vs. sealed enclosure. Ported enclosure will be more effecient but boomy. Some manufacturers overcome this by using bandpass type sub enclosure and hybrides. Yeah, too much details. The sealed enclosure requires more power but is more accurate bass. Kinda up to the person. Hope this answer some of the questions.