Certainly not. There are people who use a power amp for driving the (easy-to-drive) HE1000se or even the Utopia and swear by it. A while back I have auditioned the LCD-4 with my original Hugo and had no complaints. The extremely unsensitive Susvara (which according to some definitely needs a speaker amp) sounded better driven directly by the DAVE than via the powerful HiFiMan EF-1000 amp designed for it. I suspect in some cases it might also be a psychological effect in that having to turn the volume regulator almost to max feels like underpowering. And in some cases people simply like the added harmonic distortion leading to increased authority and «bass control». In any event you will lose transparency and resolution by adding an amp to the Hugo₂. In turn it may provide some forgivingness with respect to tonal flaws (from the notoriously nonlinear sound transducers).