Those hi-x55 have impedance of only 25 ohms. Should be super easy to drive even by a smarphone. The top hifi enthusiasts with the huge amps would frown though.Nothing expensive, a pair of Teufel Aureol overears and a Marshall Major II for work.
I‘m currently looking into these
Hi-X55 - Austrian.Audio - Professional Over-Ear Closed-Back Headphones
Austrian Audio's Hi-X55 Professional Over-Ear Headphones. Designed, engineered and manufactured in Austria featuring proprietary High Excursion Drivers.austrian.audio
Ex-AKG guys and built locally 15min from my doorstep, but the shop is closed due to lockdown