Please read the thread there is a list of known to fit speakers(in the speaker section) and you will
need speaker adapters for most.
I believe Technic is selling adaptors and other hookup kit stuff like his
famous amp harness and factory connectors.
Speakers alone don't offer a lot of improvement in anything but a L7 system
because of weak amplification. In fact your volume will go down if you are replacing the stock 2 ohm speakers with 4 ohm or higher.
In the coupe the speakers that fit are Jehnerts, Focals, and BSW and I don't
think they require adaptors.