coming back to this.... Earlier I wasn't at home so background noise got in the way of my test:
I am now at home with the B&Ws having set ANC off, but also comparing to a pair of Sennheiser wired headphones. I now hear what you are talking about.
This particular track is a really bad fit for the B&W sound signature. The lushness which sounds so good when listening to unamplified instruments really doesn't work with all the synth happening in this track. The smaller soundstage and more closed in feeling of the B&Ws dramatically changes the experience of the track. I agree completely that at least on my Sennheisers there's no comparison.
The B&W interpretation is awful at lower volumes too, muddy is a good way of putting it unless you turn it up (still 6/16 needed on the volume on this MacBook for that even at home). Even then, it's still closed in, but everything seems to be present. Other headphones don't have such a drastic change after you tweak the volume.
But in conclusion: If this is your type of music, and you particularly want that treble airiness in the synth, then the Px8s are not the right choice for you. Try something else.
Extra test: The sub-bass on this track was mostly missing on my wired Sennheisers, and it's there but as notes rather than a physical experience on the B&Ws. But on my Bose QC Ultras there's more of that Sennheiser neutrality (with less ambience/airiness) but with a very healthy dose of physical sub-bass. A completely different sound (and probably the most enjoyable of the three for that bass alone).
I'm keeping this track as a test track, thanks. The way it completely changes depending on which headphones I am using is really neat.