Laura,
The Bose speakers are wired to the Bose amplifier that I referred to above. If it works, you can use any analog audio input to it for surround sound. The original dash radio used the Bose system for speakers, so to listen to the dash radio, you had to have the stereo switch turned on.
To solve your surround sound issue, you need to determine what is left of the original system, and what condition those components are in. Then you can come up with a system to meet your needs.
Gerald