Is this the system you have?
http://www.ebay.com/itm/Bose-10-Piece-N ... 2548.l4275
Or do you have something else? I don't see anything about tweeters in the rear.
So far you've only found one blown 6x9 speaker in the rear. Is that right? If you liked the system before and if the rest of the system is still in good shape, then I suggest just replacing the blown speaker with the same thing, used even. Bose makes good stuff. I see them for sale on ebay for pretty fair prices.
The speaker I'm thinking of and looking at is a component speaker, not a co-axial, so my story changes if your system is different. Basically, you want to match up your speakers to the rest of your system for good sound and I'm not sure what system you currently have.