Which recorder for making Mixtapes, Sony WM-D6C or Sony TC-D5s?

That could have been due to the infamous "loudness war" https://en.wikipedia.org/wiki/Loudness_war
The irony was that in the 1980s Dire Straights "Brothers in Arms" was described as "the CD that sold a million CD players". Look at an oscilloscope trace of that and it was flat-lining most of the time. The reason it was so popular amongst HiFi salesmen for demonstrating CDs was that it contained so much silence between the guitar notes, silence that would have highlighted tape or record noise on other formats.