I guess it is an impedance issue, yes.
The bass is incredible, powerful and deep down to 53 Hz. There's an additional passive bass radiator on the back. Outshines the Bose speakers of that size with respect to bass.
Yes, I can return them within 14 days, maybe I will, but I'm going to try some other types of adapters and cables via headphone out first. (But it isn't a faulty cable, I rechecked that).