Ah yes, DirectStream Digital. I think the math behind that was solid but there wasn't really any point because PCM was totally sufficient. The company I was working for made AD and DA converters for recording studios and film so we were adjacent to all the insane HiFi stuff but didn't really interact with it. We did get bug reports that were real but effectively not visible, I learned a lot about debugging from watching my boss work on those.
In my foolishness I bought such a pen. It was a fun thing to try with friends for maybe £10.
Freezing CDs was another one. We tried that too. We were probably mildly stoned for that.
This was the early nineties. It was an interesting time in Hifi. 1-bits DACs and other fun marketing blurb.
I listen to CDs almost daily, on the same amplifier I had back then. I still have the CD player but it needs a new laser and controller board.
I laugh to myself every time I pull out a CD with a green edge. It's a lovely reminder of my young self and my friends in our late teens.