If your memcpy did “screw up some bits” you would have much bigger problems running the app than poor sound quality.

If it screwed up some bits you would have a useless memcpy and your applications wouldn't work, but as far as audio is concerned you have the additional problem that, unlike what audiophiles believe, it's not like those bits would always be the least significant bits.. it could as well be the most significant bit and anything in between, in other words you would get crazy horrible sound squeaks and not subtle changes in stage perception or whatever it is the audiophiles are talking about presently.

That shows how important it is to control for all variables. I understand it is difficult to match volume/loudness when AB testing speakers, amps or codecs and that might subtly influence someone’s judgement.