Here's a review where they compare the stock vs. a ModWright "Truth" unit:
http://www.theabsolutesound.com/articles/modwright-oppo-bdp-105-with-truth-modifications/
The comparison with the Esoteric player was a nice bonus. Now I'd like a comparison of the Audiocom vs. the Modwright vs. the Arcam UDP411 one of the commenters mentions.
I'm glad to hear that the DAC and clock in the stock unit are considered top-notch, in addition to the Oppo's reference-quality video processing. I wonder if Oppo buys samples of the modded players for R&D in their upcoming products.
Stock, Audiocom, Sound Affairs comparison:
http://peteswrite.blogspot.ca/2013/08/modified-oppo-blu-ray-player-audio.html