changing just the speakers in a Bose system is really opening a can of worms... it leads to one thing after the next. The Bose speakers run at 2 ohms... most aftermarket car speakers run at 4 ohms... so essentially the new speakers will end up getting half the power the 2 ohm Bose speakers were getting, thus making them not perform very well, and they will be much quieter than the front speakers.

If you just want to add some low end, get an Infinity Basslink, they are kinda pricey at $400... but they are sooo easy to install, and they really do sound good... there is a total of 6 wire connections to make... 2 (+ & -) to each rear speaker, a power wire to the battery (which I believe is supplied with the unit) and a good ground. The unit senses the audio signal from the speakers and automatically turns on.

Great unit!