Alright, my husband and I are having a 'discussion' about this one.
I know the technical numbers crunch of how it works, you sub your performance roll for the appropriate skill roll. The question is, from the perspective of the bard, HOW does the bard make the substitution? Oratory, Acting, yeah, those are easy. It's the intimidate from percussion that we're fighting over, likewise diplomacy from singing. He says I'd have to actually be drumming to use the switch (which how the hell are you going to use it for handle animal? That'd scare most animals.) or sing my argument if I want to sub singing for my diplomacy. Most of them are easily done, like dance for acrobatics and fly, but... string? Wind? How can you make a diplomacy check while blowing into a reed?
My argument (for the percussion, at least) is that I'm using the rhythm of my words, sort of a verbal drumming like rap.