To reject hard to drive speakers would be to reject many a great sounding speaker. Some speakers that appear hard to drive from a quick glance at basic specs, turns out they are easier to drive than first thought. All depends on where the dips in impedance exist, among other parameters/measurements take the JBL 4309’s for instance....they look to be a difficult load @ 4 ohms and 87 db...however , in real world listening conditions, they are seemingly a pretty easy speaker to drive, based on most positive reviews I’ve read about them.