You can do this.
The radio has the pre-outs for each channel as the Bose-system use them.
It is in the big Connector No 1 with 20 pins inside.
Mini ISO yellow preout to BOSE-Amp :
1 - Line-Out für Lautsprecher rear left
2 - Line-Ausgang(=out) für Lautsprecher rear right
3 - Line-Ausgang ground
4 - Line-Ausgang für Lautsprecher front left
5 - Line-Ausgang für Lautsprecher front right
6 - switched plus for Amplifier
Hope it helps