We did this hike in April of 2011 with Innova Travel/Innova Peru and were pretty happy with how that worked. There are lots of variables, though, and we were very happy that our family of four people was the whole group. OThers had up to 20 people in their group.
There's a complete report on our website, if you are interested. And I'm happy to answer any questions you might have.
Here's a link to our info: