Probably overdriving the next device in the audio chain
It was a little muffled, lacking detail and resolution.
Knghifi,
Many people had that experience. This Benchmark DAC1 is primarily a pro product and belts our a much higher output voltage (much higher signal levels) than layman/consumer audio systems. The reason for this is that pros need to deal with even greater dynamic range than consumers and use higher specification equipment (allows a greater dynamic range above the noise floor due to much stronger analog line level signal).
If it sounded bad and muffled then it was probably overdriving the next device in your audio chain. This would not occur all the time during soft notes but it would sure screw up transients with brief but louder peaks.
Benchmark actually modified their design in order to REDUCE the signal levels so that this does not happen to consumers. There are padding resistors inside the newer models and they set these at the factory so that the signal is reduced by approx 20 dB - so that it does not overdrive consumer gear. By removing the padding resistor you can get the full benefit and dynamic range of the Pro line level signal strength (but you need gear that is equally competent).