The response for REL regarding subwoofers

The response from REL regarding adding a REL Subwoofer for Cornerhorns.

"Unfortunately a speaker with that kind of sensitivity is going to be near impossible for any subwoofer to match with. The 2 volumes will never be able to match well. "

Is that true?  It doesn't sound true to me.  The SPL to power will be steeper than a less efficient speaker but it should jut be a matter of adjusting a powered subs gain curve to match that of the high efficiency speaker output or just using a more sensitive driver in the sub.

To bad I really wanted to buy a REL sub but I guess I'm not understanding how speakers work.