Get a 4 channel amp, and use the line inputs. If that bose uses regular speaker wire to send signal to those speakers, just cut wire and run it to your 4 channel amp as a high level input. Then from there you can power 4 speakers. Bose usually has weird impedances for their speakers sooo....running other speakers directly to that could blow them. Not sure if this would work but noone posted so its worth a shot.
