For really high quality audio you pretty much need high impedance headphones, and I don’t think these walkmen support those. I’m not convinced the new walkman sounds better than an iphone, but I’d be interested in a blind comparison test.
Pray tell why high impedance makes sound better quality? From what I gather studio headphones have higher impedance due to sharing a signal between lots of people, not for quality reasons.
I don't know how to read specs for these, but this NW-ZX707 model supports up to 50mW/ch for 3.5mm stereo and 230mW/ch @ 16 ohms for balanced output - yes it has both 3.5mm unbalanced and 4.4mm balanced TRRS on the device.