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 3090c's nominal impedance level is 6 Ohms but can go down to as low as 3.7 ohms. 8 Ohms is pretty much the standard impedance amongst stereo speakers and amplifiers so Q Acoustics 3090c is not considered a difficult to drive speaker from Impedance perspective.
Q Acoustics 3090c has a sensitivity of 92 dB. 92 dB of Q Acoustics 3090c is considered a high sensitivity compared to average stereo speaker which makes 3090c an easy to drive from Sensitivity perspective.
Read our detailed Q Acoustics 3090c Review