Our ears are incredibly sensitive sensors and I think attributing warmth to soft clipping and dampening the top end is not a complete picture.

Also warmth is just a single quality. I have a pair of very accurate “cold” headphones that I prefer for music and a pair of “warm” headphones for electronic music and gaming.

Past the headphones, it is not so much warmth as it is space in the sound for me. My headphone amplifier sounds effortless and that’s the best way I can describe the quality of what I hear.