Women Singers – Is it preferable that women attend a performance by a male or female singer?

Is there a prohibition of Histaklus of a woman staring at a man performing? What about “Kol Ish” in hearing a man sing?
Is there a problem posting videos of women singing online? Does a “Kol Isha Warning” help?
Do female performances not reflect “yiddishe values”?
Where do we draw the line of Tznius in public?