The output from the Sony headunit won't be anything like what they claim - you'll probably get about 15W per channel before you start talking about serious distortion. Most aftermarket speakers need more than this to run successfully, and sound quieter than OEM speakers for a given input power. They're probably blown because the previous owner didn't realise that aftermarket speakers should be amped.. if you go out and buy some more, without amping them, you'll probably end up doing the same to your new speakers.
Personally, I'd sell the 6*9's, take the cash, add it to your money already budgeted for the replacement fronts, but some uprated speaker cable, sound deadening and a better set of components, and install them running off the amp that was driving the 6*9's.
No damaged 6*9's caused by the bass trying to escape the boot via their cones then, nothing blocking the bass from coming through, no high frequency stuff being played in the back and confusing the music, and better quality sound up front. You really can't lose going down this route
HTH
Mark
Personally, I'd sell the 6*9's, take the cash, add it to your money already budgeted for the replacement fronts, but some uprated speaker cable, sound deadening and a better set of components, and install them running off the amp that was driving the 6*9's.
No damaged 6*9's caused by the bass trying to escape the boot via their cones then, nothing blocking the bass from coming through, no high frequency stuff being played in the back and confusing the music, and better quality sound up front. You really can't lose going down this route
HTH
Mark
