You didn't say if there was anything wrong with your Bose. If some
part is broken then you will need to fix it, or replace the entire system.
However ... if you just want better sound. Try this.
I listen to Rock and the Bose just didn't put out enough sound for me.
A local sound shop outlined what I could be getting into if I replaced
the entire system - 4 spkrs, subwoof, amp, cabling, $1000 +, and that
doesn't include a new head unit or install. Major PITA with the front
(door)speakers too.
He reasoned that I would need a subwoof in any event, so he suggested
adding a self-powered subwoofer to the existing Bose unit. Then see
if I still needed more sound.
This was a great idea ! He installed a Kicker 8", easily connected to the
rear Bose speaker INPUTS, has its own amp, mixer, and crossover, and
relative volume control. It was just the thing. The Woofer volume is linked
to the fader, and the extra Bass did the trick.
I no longer am interested in replacing the Bose system.
Cost - $250 including the install.
BTW - while reading the FSM about the Bose system during this
process I found that it is recommended to set the Treble and Bass
controls to MAX ! Turn them down only when or if there is any
distortion. This also made a big difference in the total quality of sound.
HTH