The Denons aren't middle ground, they are bass emphasized. DT880s aren't mid-emphasized either, maybe coming from D2000s they will sound so but they should be considered neutral, much like Sennheisers HD800. D2000s had more sloppy bass than the Pro 900s however the Ultrasone had a much higher volume of sub bass. For bass heads I'd suggest the Denons for Hip Hop and DnB and the Ultrasones for EDM, faster techno that sort of music.
I haven't heard the Nuforce HDP but chances are like most cheap sources the sound will be somewhat congested and lack detail at both extremes, you may disagree now but as you scale up you'll understand what I'm talking about. It was only a couple years ago that I was content with my cheap source and D2000s. With this in mind as you upgrade and hear more details your views on the Denons may well change. I also believe the more you listen to music you'll find you want neutral, something you may have found dull at the start of your audio journey.
I've messaged Dave Rat in the past and he's a bass head, as I've said previously and to him also is that the majority of headphones will drop lower than human hearing on a good source. The ONLY reason Denons are preferred is for there heightened bass which is a couple of notches louder than the rest of the spectrum. Another way to test this is to run a bass slide on TTG and you'll find the Denons create the woofer-like vibration sound sooner than neutral cans. This is not only enjoyable for a bass head but upon listening you would get the idea that they extend further, they don't. Likewise this is why when moving from a Denon to something more neutral you would find them not only mid-centric but bass deficient in comparison. Likewise if I go from listening to my DT880s to the RX700s I find the JVC's very warm sounding and bass heavy.