"Fact is though, on A'gon it seems that most comments about the Benchmark DAC's have been negative."
Perhaps because most of people seek very warm sounding gear. Let see what Benchmark's Technical Director John Siau said about it:
"We designed the DAC1 for maximum transparency. If you want to add warmth, you can't add it with a DAC1. Personally, I do not like what warm sounding equipment does to the sound of a piano. Warmth is wonderful on vocals, guitars and certain instruments, but it beats against the stretched overtones of a piano. The overtones in a piano occur at slightly higher than harmonic ratios, and these create beat notes with the exact integer ratios produced by electronic equipment (and speakers). Too much harmonic distortion will
make a piano sound out of tune."
That would suggest to me that warmth is not a virtue and more experienced listeners, including professional reviewers prefer neutral sound. It is also likely that rest of the equipment they use don't have many faults that Benchmark ruthlessly reveals.