option 5 pull the plugs off the back of the mb speakers, mount an amp in the boot/somewhere, run from amp to speakers as normal fit the empeg under the dash as transmitter plan and run RCAs to amp.
When time comes to sell car whatever return plugs remove empeg and you be back to norm.

You can also get modules that take a high level output from speakers and drop it down to a low level input for an amp so you could take a feed from one of the speakers into this and then into empeg aux and you have anything that is piped to them from mb system such as sat nav commands.