Well, i'm glad i was wrong about the line out, using the DAC on the TWL. :)
On the TWL: 16-bit Linear Audio Stereo DAC (96 kHz, 48 kHz, 44.1 kHz, 32 kHz, and Derivatives) not that bad, some onborad audio cards are still 16-bit
Anyway, saying that the amp reduces the quality can be subjective...