It seems like you are arguing with someone that 32 bits per sample is too much resolution and I agree, but I'm not sure who you are are arguing with or who is saying that.
The point isn't that you shouldn't record audio at 32-bit depth (which you probably shouldn't if you expect it to bring much benefit, but that's by-the-by), it's that even if you did, and you have a 7.1 system with 8 uncompressed streams, you still won't be anywhere near the point where USB 3 cable grades will start to matter.
You're the one who asked for clarification on the footnote specifically.