Thanks for the comments, I'm glad I could be helpful in your search.
I see how my two statements seem contradictory. Maybe I can clarify:
The first part, where I say the Cube is slightly more lively up top, I'm talking about overall extension. Both do highs pretty well for such low priced units. The Cube has a touch more energy up there but as I said, not a huge difference overall.
The next part, where I say the Cube is warmer overall and the U100 more focused on upper mids/highs, I'm talking more about the big picture. Even though the Cube has very slightly more sparkle, it also comes across as thicker/warmer/more musical, or however that is worded. The Cube comes across as more light/fast/sparkly/detailed. Does that make sense? You could say that the Cube is too thick on the bottom end, or has a slight U shaped curve, or you could look at it as the U100 being too thin down there. It's a matter of perspective. Again these differences are not huge.
Neither unit is 100% neutral. The U100 probably comes closer but it is a very small difference.
Hope this helps!