One finds orthodox performers who sing for mixed-gender audiences (eg recently)
However, one also finds achronim who call this assur.
I'm curious for a bit more explanation of the sources/reasonings behind the two positions. (Obviously Gemaras like Sukkah 51a discussing the temple balcony are probably central, but I'm interested specifically in how both positions apply that precedent here, and which contemporaries speak about the issue.)
A previous question didn't address gender aspect specifically - Going to classical music concert.