ibasso uses a better dac chip. I don't know if it sounds better because I haven't heard it (I own a Total Bithead).
According to the ibasso D2 Boa thread, shipping is VERY fast. Either one would sound good, but if you are only going to use your computer, then I would hold off until you see how it sounds. The advantage of a protable amp with a built-in dac is that you can get great sound out of ANY computer you happen to use (at school, the library, at work).
I think the Total Bithead sounds great with the AH-D2000, but I have a feeling the D2 Boa might sound better. I'm not willing to pay to find out though...sounds pretty good now.
synaesthetic is correct about the horrible layout of the Total Bithead for portable use, but I only use it for the computer, so it is always sitting on a desk where the layout does not matter.
Scott