remeber with horns your can cross over usually from 1000-1500, some go as low as 500. So really you are looking for something that plays better midbass and can extend to 2k or so unless you want something to play higher so you can swap out the horns someday.
The ca18rnx i think is a good choice. Just make sure you are matching you levels corretly.Personally i might prefer the Brother driver,i think la18rnx? Its very similar ony it has the aluminum cone. Slightly better detail and lower extension, but it breaks up after about 2k. But again with horns you usually cross over much lower than 2k so youll be fine.