x2. In fact I find the timbre more correct using flats. With bowls it's true, as Stretch said, that sound is airier and more expansive, sort of more detailed, but I personally find it a bit less "believable" with some instruments and voices. Anyway, with both they sound damn good.
Unfortunately I've never managed to listen to the HP1, so can't add anything worth to the original question. It's said that both use the same drivers, and these were selected into the same matching tolerances, so my take is that they'll sound very very similar. Pure speculation