Well I have been using the Denons for a week now, and thought I would update everyone on my experience and feelings towards both sets of headphones.
I have used both pairs with my laptop via a Nuforce uDAC2 and also directly out of my iPad using Lossless in iTunes and Spotify.
The Denons are a really well built pair of Headphones with a very long cable for ease of use...however this can be a bit of a pain when listening within close proximity of either the Laptop or iPad. The Denons are extremely comfortable to wear for long periods of time without causing any heating or sweating on the ears. Very good at cancelling out outside noise and leak very little indeed.
They provide an open sound (for closed back headphones) and I find are especially good with vocals providing a clear insight into the music. The Bass is strong with good mid range and highs.....I had read that they can have a tendency to sound sibilant, however I havent found this personally. My only main concern with the Denons is that sometimes the Bass can seem to be a little overpowering, especially when used with the uDAC2 and Laptop.
Overall these are a good headphone wich provide and insightfull and enjoyable listen to a variety of muscal genres.
I have owned these headphones for about 5 or 6 months now and have listened to them extensively with laptop alone, laptop and DAC and with my iPad. Build quality looks poor, compared to the Denons and the can become uncomfortable after a few hours listening. Being an open backed design they leak noise like a B***h and are therefore not ideal for listening in close proximity to other people (which can be a problem for me), they are also not very good at cancelling out external noise.
However I find the Grado's to be a far more enjoyable listen, with an extremely airy and open sound, I find that they pick up a lot more of the intricate detail of the music compared to the Denon's. Personally I dont find the Grado's lacking in bass like some people....dont get me wrong there is not huge amounts of Bass, but you know its there and for me they are just right. People have also commented on the treble of the Grado's, but again I have never found these headphones to be shrill or tiring over longer periods. Currently listening to Wilco's the Whole Love, a 96kHz 24 bit download from HD Tracks via my Laptop and uDAC and the sound is clear, open, expressive and detailed.
Overall I would rate both pairs of headphones highly for a variety of muscal genres, and both have a place in my life, depending on what I am listening to and where I am listening. Personally if I was told I could only have one pair of Headphones I am afraid (probably to some people's disgust) I would opt for the Grado's 9 times out of 10. There open and extremely detailed and to my ears well balanced sound wins out over the downsides of not being the most comfortable and leaking sound.