I live for the split second a band member, in the middle of the performance, says "Whoa!", surprised by something another band member or even himself or the audience did.

Whoa! These guys had seen pretty much everything on the road. Every excess, past every limit. "Whoa!" takes another meaning in that context.

That whoa! is unexpected, it's revelation. It's ecstasy, almost orgasmic. It's hitting a home-run blindfolded.