You need a crossover for the comp's tweeter. If you put the coaxials in where the mid was (crossover still wired), it'd play the same range as the comp did, and its tweeter would probably not work. I'd try that. Or maybe even snip the wire off the coax's tweet.
1999 Buick Park Ave Ultra
Head Unit: JVC KWHDR720
EQ: Audiocontrol EQL
Front Stage: Hybrid Audio Technologies Imagine 5.25 mids, Morel Maximo tweets
Sub Stage: Boston G3 10", 0.5 cu ft sealed
Amp: PPI Phantom 900.4
Rear Fill: Boston SE953 6X9's