OK, quick primer...
from a sound quality point of view, one of the worse things about the stock Bose system is probably something that many don't even realize...
when were talking about sound quality, the criteria that makes up quality audio reproduction can be stated as sound stage, imaging, frequency response, tonal accuracy, etc.... the idea is to be able to replay a recording as it was recorded & as it was intended to be listened to. if you close your eyes in a real competition car, you should hear the performance like it was happening in front of you, it should sound like your up front & center at a concert, the performance is happening in front of you, the drummer is further back than the vocalist & maybe off to the left, everything should have a definite place that it originates, & should sound real, lofty goals for any system, but the closer you can get to this the more quality of sound you'll have
now tonal accuracy & frequency response there is only so much your going to do with the stock Bose... if you really want an audiophile quality system then the stock bose needs a whole lot of help, really everything needs to be replaced.... but, if it at least had half way decent imaging & sound stage it might not be too annoying to listen too at least...
to me, the biggest deficiency in the stock system is there is no sound stage, there is no imaging.. it is just a mass of noise coming from all over, it is so annoying to me that I hardly ever listen to it, the only music I have available to me in my fx is my stillen headers & exhaust, cause what comes out of the stock bose is not music

. to have any kind of sound stage & imaging you'll need to turn the rear speakers all the way off, fade it all the way to the front, most competition cars either have no rear speakers, or if it does, they will be turned way down & delayed to just add fill, the rears should just play what would be the sound that would bounce off the rear wall at a concert if rears are used at all, the stage itself should be in front of you, if you close your eyes you should hear the performance like it was in front of you, you should be able to locate precisely where the singer is in relation to the drummer, in relation to the sax player, etc... you should be able to, with your eyes closed, point to exactly where you hear the singers vocals coming from, not there or there, but right there.. this is called pin point accuracy & in a good system, you should have a nice wide fairly accurate deep sound stage, it should not sound muddy or like the vocals & everything else are just coming from all around you, if you don't know any better than this might be what you expect to hear & have become accustomed too, but it is far from correct & far from sound quality...
one problem is that our sub woofer is referenced to the rear speakers, big flaw on Bose' part, because if you turn the rears down to clean up the stage, you also drop all lower frequency response out of the picture, you loose the sub completely... a very sad thing to listen to when your looking to listen to music....
by just adding an epicenter & referencing it off of the front stage drivers, that alone would be a huge improvement in sound quality, just because you'd now have the ability to turn the rear speakers all the way down & still listen to your front stage while also still having the lower frequencies played by the sub... this alone, even if you never turned the epicenter on or never used it's restoration circuit, will be a huge improvement in the sound stage & imaging... enough to maybe make it bearable to listen to at least...
........