Daniel, can't tell if DACPort would be an upgrade from the HRT Streamer II.
What I can tell is the synergy DACPort with Ultrasone Pro750 is quite sweet.
I am surprised by Larry's remark above finding the DACPort warm. I find it quite neutral, forward positioning, with great presence of the mediums.
Given the dark profile of the Pro750 (I understand this is even more pronounced on the Pro900), this is a nice combination. It definitely works well with the Pro750, I'm expecting the same with the Pro900.
I don't find it warm either by me baseline. Maybe compared to something quite bright.