Compared the DAC sections ? No. Hooked the Oppo to the M51 for sonic bliss ? Several.
Here's one I had my manservant type up earlier:
There is also a discussion of the Oppo/NAD combination in the early pages of this monster thread and another via Google (BDP-83, from memory).
Yes, the DAC sections. I read the article you linked, but again the Oppo was not compared to the M51 as a DAC. I'm surprised several have the Oppo hooked up to the M51 without testing/ commenting on the DAC section differences?