Alright, as an owner of both, I will give my take:
They are the same headphone down to a couple specific things. One is the driver housing is a different shape. It could also be of a lesser quality plastic on the Aurvanas, but Creative did a very good job making them "not look cheap". The materials and shape could account for the *very* slight sound signature differences. The headbands are virtually the same, although I prefer the band on the creatives because it has a better grip on the swivel of the cup forks. It may just be that my Denons were "loose" but I like the fit of the Aurvanas.
The earpads are the same shape because the driver and driver baffle are the same. this is what is exactly the same, the driver and baffle, also the wires that come into the cups are of the same guage. They have slightly different ways of holding the cord down, but that is a side effect of the cups being different. While the pads are shaped for the same baffle, the Aurvana pads are about 10-15% more plush. It is something only noticed when you have them both and swap between. I like the Aurvana pads again, so headband (well really just the swivel) and pad win for Crearive.
The inside shape does, indeed, reflect the different cosmetic look of the cups. This is where you probably get the different sound. Denon's more egg-like, and a plastic that seems a bit harder, while Creative uses a softer plastic and a slightly larger volume inside.
The cables on both terminate to a mini-plug after a short distance and expect the use of an extension cable for extending the length. This makes them both very mp3 player friendly, however, Denon's plugs are much better than Creative's, but that is not saying a lot, as even the Denon's far superior extension cable is pretty weak. Most people chunk it, and the Creative one isn't even worth the materials it is made from. It is so sad. People say the Denon's cable is an issue, well Creative's extension, same length, is a full 1/2 of the size of the Denon. It looks like it could break if you pulled on it a bit too hard. Needless to say, the cable, 1/4" adapter, and plug terminations are much better from Denon. They get you by, and work OK as a complete kit, but the Creative's are trouble.
I modded my Aurvanas over the Denons. I am happy that I did too, and the next mod will be a re-cable, but the cable is the same as Denon until the termination/plug, so it sounds fine with a good extension. The Aurvanas now blow away the stock Denons, but some people may not like it. The cub design and material quality lend extra HF extension to the Denons, but the bottom end suffers a bit, where on the Aurvanas, the entire sound spectrum is shifted down a bit. Slightly less HF exstension, but a bottom end with some weight to it, and after the mod, a somewhat "inspired" one from the mod of the D2000s, the bass is extremely taught, while the midrange remains about the same. Voicing is good on both, but there seems to be a bit more "air" on the Denons, however, I have grown to realy like my modded Aurvanas, and I don't even pull the Denons out. I will probably mod them eventually and be even more impressed, but until then, the sleek piano black with stainless steel accents (real or not) on the Creatives, they just fit well and look damn good when I hang them up. They have become an extremely fun pair of phones.
The velvety bag you get for the phones is interesting in that The Creatives actually have a stitched tag on theirs with the Creative name, but the Denon bag is just that, slightly less weight, and no tag, but looking the same. I know that is getting into the nit-picking, but I wanted to writeup basically a primer that sheds light on these two phones, made in the same fatory, by the same company, with the same important hardware, except for some cost saving on things like the plugs by Creative, an effort to keep the two brands separate from one another, and perhaps some slight material/design engineering changes that favor the Denons, of course, they are often an extra 50 dollars, and even more, so knowing all of this, I see no reason not to try the Creatives if less than 1% performance change (without the extension) is not an issue.
