I also have the Benchmark DAC2HGC. Here is how I was able to get this to work:
Go to the Audio Options Screen. For Audio Device, Choose Benchmark_DAC2 ASIO Driver.
Go to Device Settings (immediately below the device selection). It will pop up a new window with 4 sections (Device, Buffering, Volume, Tools). In the tools area, there is a checkbox next to an option which says "DSD bitsream in DoP format". Check that box.
Doing so allowed SACD's to play.
You can also consider going back to the Audio Options screen, and choosing "DSP & output format". In the drop down box labelled "Output Encoding", chose "DSD in DoP format (requires DSD capable DAC). This will upsample all formats to DSD output.
I've been very happy with this combination of settings and sound. I'd be interested in what other Benchmark DAC2HGC owners have found to provide the best quality in their systems.
Good luck!