The Denon headphones were also made by Fostex, so there's definitely bound to be similarities in sound and design, though just how much is still a bit unclear. As for the coloration of Denons, it varies by model. The D7000 is probably the most relevant here however. It has a robust bottom end with quite a bit of punch (though it's less substantial---and also less bloated---than the D2000/D5000), sparkly and moderately bright highs, and a somewhat recessed midrange. I'd say it's a somewhat energetic signature while still remaining pleasant. It has a certain "cinematic" quality that lends the D7000 to home theatre use, but it's also certainly good with many types of music in my opinion.
Supposedly the TH900 is more detailed and has a more expansive presentation, but some have complained about the mids being even more recessed. I suppose we'll see soon enough!