It's all subjective. While I generally see 2 TODs go off, it would (I'd guess) be about 50% of the time at best. I'd say I get single strikes 35-40% of the time, and multiple (from 3-4, I think I've hit 5 a few times but never really confirmed it in teh combat log) the rest of the time.
That being said, i admit I've never actually kept track of the results, trash dies too fast and I'm usually busy trying to inflict as much damage as possible on the bosses, so my perceptions could be wrong.
actually from what I've heard, fire stance has been broken lately and getting a doublestrike bonus just like grandmaster wind...
Really though the multi-strikes depend a lot on what part of your attack chain you activate them on. on live one part of the chain gives 1 hit while another gives 4 :\