Both are decent but sound very different from each other. The A40s will be more bass heavy, but not to the point where it's bloated. They have a warm sound signature as opposed to the 363d (essentially a rebrand of HD 558s) neutral sound signature. The 363d should be more comfortable and have a wider sound stage since it's open back and uses velour pads. Because of its neutral tone the 363d should also have greater clarity and positional queues such as footsteps should be easier to pick up.