There are two main factors that set how easy or difficult a speaker is to drive, these are Speaker Sensitivity and Impedance. A speaker rated lower Ohms requires more current than a higher Ohm speaker. Similarly, a speaker with lower sensitivity requires more power to reach the same volume as a speaker with higher sensitivity.
Klipsch OJAS kO-R2's nominal impedance level is 8 Ohms but can go down to as low as 4.2 ohms. 8 Ohms is pretty much the standard impedance amongst stereo speakers and amplifiers so Klipsch OJAS kO-R2 is not considered a difficult to drive speaker from Impedance perspective.
Klipsch OJAS kO-R2 has a sensitivity of 97 dB. 97 dB of Klipsch OJAS kO-R2 is considered a high sensitivity compared to average stereo speaker which makes kO-R2 an easy to drive from Sensitivity perspective.
Read our detailed Klipsch OJAS kO-R2 Review