They're right to an extent.
To start you would need to go with an aftermarket headunit to have the ability to add an AMP and go about creating the setup you need. And replacing the stock headunit with an aftermarket one sure doesn't seem like an option, so you'd have to find somewhere to mount a 2nd headunit, which from how it's looking so far... there's just no where to do that. at least without doing any major changes.
To start you would need to go with an aftermarket headunit to have the ability to add an AMP and go about creating the setup you need. And replacing the stock headunit with an aftermarket one sure doesn't seem like an option, so you'd have to find somewhere to mount a 2nd headunit, which from how it's looking so far... there's just no where to do that. at least without doing any major changes.