I don't have any MiniDSP product, but please don't think that you are being cheated by the company.Hello bennetng,
I finally got round to doing this test. To my surprise the volume control in the MiniDSP NanoAVR did not pass the test.
This was a big surprise, because I assumed that the 32bit floating point SHARC processor would not work this way.
Every step in the signal chain needed to be in float until volume change, so if the file decoder, playback software, driver, firmware etc... even if one of them is not working in float before reaching the float capable DSP processor, then clipping will occur.
Therefore I always recommend adjusting digital volume in software as early as possible.