If my car didnt come with bose i would have swapped it out. Im not all for big boot builds.
My set up was small but pure quality.
I had a JL Audio 8W3V3 In a highout put enclosure, Focal 165 Anniversary components front and rear, One single amplifier JL Audio XD600/6.
Weight: Whole System Within 15KG.
It sounded amazing, the little 8 really sounded class, The focals were full of clarity and the amp was slotted under the seat.
It got loud aswell, my mate has this exact set up in his R32.....It really does sound amazing.
After all of that though the BOSE is very well designed, i now sit in my car with the bose and yes its not as loud but it retains quality which is most important.