To be honest there's lots of little factual inaccuracies in that piece. The notion that the A600 was "fully software-compatible with the A500" just isn't true.
Similarly, claiming that the SoundBlaster had "22 voice sound" vs the Amiga's 4 voices. Yes, later SBs had a 22 channel FM synth chip, but that's not remotely the same thing!
It would have been more accurate to say that as PCs became faster they became capable of mixing multiple audio samples together before playing them through a stereo (ie. "2 voice") DSP - using the greater CPU power to match (and, eventually, exceed) the Amiga's sound capabilities.
In general, I suspect the author is misunderstanding secondary sources, rather than misremembering first-hand experience.
The Amiga's audio reproduction is an odd beast. Incredibly sophisticated one hand then completely hamstrung by the fact that stereo planning has to be done in software. So you either run it as 4 independent mono channels, or you devote lots of CPU time to software panning, which rules doing that if anything else CPU intensive is going on. So you basically can't have stereophonic audio in games.
