The audio in the SF2 review for PCE sounds a bit off (lil' scratchy/rough?). It doesn't sound like that on my copy, or B_T's audio comparison videos. Maybe he used an emulator 
Youtube butchers audio and they might not have rendered the final video with full sound quality in the first place.
So even if it was originally recorded off of real hardware, unless they jacked the audio bitrate all the way up like I did, it shouldn't sound the same.
If anyone finds any of my videos on youtube, always check the description for a link to download the full quality video. Even if a video isn't on my site, I usually have a link for it on the youtube page.
EDIT: I just watched that comparison video again and it sounds like they used a kisado to play the game while recording. Using a converter, or at least the kisado, the game has some feedback kind of noise that seems to get worse the more that is happening in the game.
Its kinda like that buzz that often happens with PSG music in HuCards that doesn't clear until a new song is played(like in the Ninja Spirit sound test), only much worse. For years I had hoped that it was only the converter and not the actual game and I was happy to find I was right once I got my first PC Engine system.
When the guy in that video shows you how to play a PCE HuCard, he only has a white PC Engine and a Turbo CD combo with a kisado. If he used either of those to record from, the audio wouldn't be clear.
It was funny how he said the PCE sfx(
kicks/punches) are noticibly worse than the SNES version, since I find that the sfx to be the PCE's greatest leg up on the SNES port. I even prefer the Genesis version's full sfx over the muffled, short/looped SNES sfx.