Its worth noting that they may be all you have to go with but efficiency specifications are quite loosy goosy typically and hard to bank on either way.
Usually, if speaker is small, chances are bass will be limited with most tube amps. Those speakers that can do extended flat bass out of a small box always require more power and current to achieve it. No free lunch here that I have ever seen or heard. If it appears too good to be true, it probably isn't. if you punt on the extended bass aspect of things though, things become pretty easy. Low bass is where all the hard work happens ie large efficient drivers and or smaller drivers and more power/current to move them. Its basically the limitations of physics that cannot be undone even with the best and highest quality designs.
