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.
KEF R11 Meta's nominal impedance level is 4 Ohms but can go down to as low as 3.2 ohms. 8 Ohms is pretty much the standard impedance amongst stereo speakers and amplifiers so KEF R11 Meta is not considered a difficult to drive speaker from Impedance perspective.
KEF R11 Meta has a sensitivity of 90 dB. 90 dB of KEF R11 Meta is considered a high sensitivity compared to average stereo speaker which makes R11 Meta an easy to drive from Sensitivity perspective.
Read our detailed KEF R11 Meta Review