The reason why it was confusing is because you are asking about two different things. An effects unit with true bypass, as the word implies, bypasses it (the Helix in this case) completely, so it is as if you don't have it connected into the signal path. In that case you're guitar signal is NOT being processed by the DSP, and definitely not by the A/D converters, of the Helix which means there is no signal degradation, EXCEPT when dealing with long cable runs. So, in order to mitigate the signal loss produced by long cable runs, you need to insert a buffer into your signal chain. As I mentioned earlier, Helix has a buffered analog bypass. This is what the video posted earlier demonstrates. But, so far, we're talking about an analog path.
Now, since you're connecting the Helix via USB into your computer, true bypass or buffered bypass is of no consequence to you. It's only of consequence if you're going from the Helix into another device. Going into your computer via USB requires an A/D conversion, which is done by Helix' converters. Line 6 says that they go down to -123dB, but they gave us no reference or frequency. Hopefully they post the full specs soon with more info on the quality of the converters found in Helix. Like you said, you will have to wait and see how transparent they really are after hearing from others, or trying it out yourself.
HTH