I received mine today and I am quite pleased. I knew about the Signature Pro as I listened to it extensively months ago and it became my favorite Ultrasone headphone, especially since it "stopped" with those annoying highs like on the Pro 900 and many other models.
Maybe I am not bassheady enough but I wonder why you would eq the bass even more (during my own eq test the Signature DJ withstood any distortion, they are really built to kill - impressive) as there's plenty of it and in very good quality as in not bleeding over anything or melting over. It's like it's own layered structure. I think someone here got annoyed with everything being too smooth for him and I suspect the bass creating that impression as it's rather subwoofer like (don't confuse with bleeding, bloated or farty)
Having a HD 800 as well I notice that there's still a league between them as the HD 800 just has more details and layers and the better soundstage. Comparisons are hard though between open/closed and signatures. All I can say is that it makes metal music more enjoyable (I listen a lot metal and most recordings are rather "mediocre") than the Sennheisers and for EDM there's no contest. Those two complement each other very well.
You might really enjoy the Vocal presentation with them as well. That was my favorite surprise with the DJ's. They have outstanding vocal presentation. Perfectly placed and soooo realistic to me. Sounded like the microphone was directly connected to my headphones.