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.
Q Acoustics 5040's nominal impedance level is 6 Ohms but can go down to as low as 3.0 ohms. 8 Ohms is pretty much the standard impedance amongst stereo speakers and amplifiers so Q Acoustics 5040 is not considered a difficult to drive speaker from Impedance perspective.
Q Acoustics 5040 has a sensitivity of 91.5 dB. 91.5 dB of Q Acoustics 5040 is considered a high sensitivity compared to average stereo speaker which makes Q Acoustics 5040 an easy to drive from Sensitivity perspective.
Read our detailed Q Acoustics 5040 Review