I'd always thought the CS-77 was pretty efficient, but I didn't quite expect it to be as high as the 108 dB listed on the spec sheet posted here. Of course I assume that's 1 watt, 1 meter, and can be compared directly to other speakers.
That being the case, it looks like a 25 wpc SX-636 would have plenty of power to drive them. Maybe I should experiment with my pair of CS-77's, and my SX-636. The CS-77's add nice bottom and presence to rock in the basement, powered with a 40 wpc Yamaha RX-series receiver.
One feature of the latticework grille that may not be immediately appreciated is that it protects the drivers beneath. Little worry about poking anything through the drivers, especially nice for those who can't resist moving and otherwise futzing with speakers.