My impressions of the DAC were through the line outs directly to the BA. I did not really listen to the pair together because I was more curious about each component separately and also because I wanted to be familiar with at least one component in the chain. The setups were as follows:
- Quattro DAC --balanced--> BA --balanced--> HD800 / LCD3
- Quattro DAC --SE--> BA --balanced--> HD800 / LCD3
- Perfectwave DAC --balanced--> Quattro Amp --balanced--> HD800 / LCD
I did however spent two days listening to headphone outs of the DAC (I brought only the DAC on a business trip). The DAC headphone outs did not have any hardness or thin treble. If anything, they lacked definition, resolution, and were a little bit dull. They sounded warm and definitely did not have any hardness or treble thinness.
I hope that helps.