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.
It was an interesting (to me) footnote to the point that even if you massively overspec your audio stream to the point of physically being unable to record the audio at that quality (the footnote being why it's unfeasible), you can still easily fit many such streams down a single modern-ish digital link.
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.
