Not sure if my response is on point, but I had a $375 proprietary mod done on on my Oppo 103 by Stereo Dave's Audio Alternative and it was totally amazing. The improvement in SQ was apparent from the first measure of the music. The noise level was substantially lowered and sound stage was vastly more expansive. I have had a dozen mods on gear over the years and none have been more worthwhile... nor more cost-effective.
It is clear that mods to the stock Oppo CD can be extremely worthwhile. At any rate, the stock Oppo players, to my ears, are the best bargain in the audio world.