http://www.digit-life.com/articles2/...e-audigy2-zs/:
This excites hope that this problem still can be solved by software. Besides, this card might have been measured with some special drivers. Anyway, this doesn't change the result. And we can't speak of full 24-bit support regarding Audigy2 ZS. Something strange resembling 16 bits is processed even through the digital path.

Pity, but we see the same picture. Though now we know the reason is card's digital part, i.e. DSP algorithms. This gives us hope they can be neutralized in the future drivers.