IIRC, there were Houx tickets available last year when the internet booking site was opened to members.
Only phantom Houx tickets, I'm afraid.
I tested the link every day whilst internet booking was members only, as did Carole, the ACO's manager in Rouen. Each time you opened the link it came up with "all seats sold" from day 1 onwards.
I did get Houx tickets from the ACO for 2011, but by perseverance, and not via the internet booking site.