Thanks, duckworp, for sharing your testing results.
I think most audio gear is so good nowadays that the "diminishing returns" thing kicks in real hard sometimes.
Your post reminds me of a time years back where I bought a new pair of speakers (JMR Trente) and wanted to burn them in for a while. My main rig at the time was all tubed and was in the $20-$30k range back in early 2000's. And not wanting to waste tube life I decided to pull out an old, 1970s Pioneer integrated for the burn in purpose.
The speaker cables I used was one of the thinner gauge copper wires bought at radioshack. And this thing was a mess! All wadded up making it hard to find the ends. When I finally found them and hooked up the speakers, it looked like a ball of yarn a few cats had a heyday with.
I had a Marantz 63SE CDP. I put a disc in to let the speakers break in. And since I was already there, thought I'd read an audio magazine and listen to the music as a background.
But to my astonishment, the music sounded pretty darn good! A sub $500 rig was holding its own.
For shitz and giggles I put on a few test tracks being confident the rig would not be able to pull out all the nuances from the tracks that my main rig could. After a few tracks I stopped, disappointed all that extra money bought so little in return.
At that time I told myself it's ok because I like the audio toys and that had I actually done a long term comparison, I would have noticed the differences right away.
But I didn't do the long term comparison just in case! ;-)