I had my first soundboard shoot recently when I shot Kelly Clarkson. I found out pretty much that day that it was a soundboard shoot, and I went into the concert hoping my 70-200 was good enough. I did try to calibrate my 1.4x extender, but couldn't get it calibrated right, so I gave up on using it.
Did I enjoy the soundboard shoot? More no, than yes honestly. What were the issues I came across?
1) Bring a stool or something to stand-on. While normally the soundboard is set on risers, or a little platform, we were shooting from in front of the soundboard putting us on the exact same level as the crowd. I'm too short to shoot over everybody when they were standing up, so ended up shooting up the aisle whenever the singer happened to walk across the stage.
2) It's much easier to get more of the band on the stage from the back.
3) You need a really long lens. 70-200 was "ok", and it was only ok because the soundboard was about halfway back. Any further and I would've been screwed.
4) Did I mention if you're short you have a problem when people stand up?
So it has its pluses and minuses, however I still like shooting from the pit better.