I have both, and I prefer the sound of the minibox D. The minibox is more balanced, while the T2 is a bit bass bloated and warm. But in terms of size, the minibox is like 2.5x larger than the ibasso T2. I paired the minibox D with my iaudio x5 because their footprints are exactly the same and the ibasso T2 with my sony A818. You might ask, "The sony has a really warm sound signature, and paired with the ibasso T2, isn't that too much?" Well, paired with the ety er4p makes a great combo, since the ety's are really cold and analytical.
In terms of power I've only ever used them to drive IEMs and grados, and they perform the same as far as I can tell.
hope that helps