I just received a Benchmark to mod. First, my listening impressions:
I can see why so many have been anamored with this DAC. It has the best HF extension and HF dynamics that I have ever heard in a stock DAC. However, the midrange and bass is inconsistent with the HF dynamics. This is just the opposite of what I usually find in stock DAC's. Generally, the HF extension and dynamics is what is lacking and the midrange is very good and the bass okay. The High-frequencies are usually recessed or at least imbalanced. In this case, the midrange and particularly the bass is less dynamic than the highs. With some classical music that contains a lot of HF information, this is hardly noticable, but other pieces that have loud kettle drums or bass viols, it is noticable.
Examination of the circuitry lends some clues as to why this unexpected imbalance is occurring. Everything on the board is surface-mounted, including the large filter capacitors. These should really be through-hole parts. Even the very best SMT parts cannot yet compete with good through-hole caps for this function. Typical bridge rectifiers are used as well. High-frequency decoupling caps are located very close to the op-amps and they are larger than what I usually see. This probably accounts for the excellent HF extension and dynamics. Another thing that I noticed is a slight hum in my system. This is typical of many DAC's that do not galvanically isolate the digital input.
Next, to do some mods.