I almost loved 7520, but the treble kills my ears and the bass is super flabby and uncontrolled. Only the midrange made me somewhat happy, and it was not quite as resolving as I expected. V6 bass rules with Brainwavz Hm5 earpads (v1, not the thicker v2 sold these days). But then those pads worsen the nasty upper mids peak. If CD900ST does improve on these details, no doubt that it rocks.