I wouldn't recommend that... The companion 5 was designed to be a stand alone, self contained 2.1 system. If you were to jerry-rig it, the power brick inside the subwoofer may not take the additional load and fail.
Best of luck!
Sadly, Bose historically doesnt publish it's speaker/power ratings on systems like that, usually just on the bookshelf speakers so you can match the watts and ohms.
That being said, I'm pretty sure people online have tested them and found what the specs read... just gotta do some deep diving!