Chingchai, unfortunately we didn't make it to Thailand this year, we went to Indonesia instead (not bad either!

), so I still need to come by to experience your tank.
I hope the achilles will accept each other, part of the trick will probably be heavy feeding, so competition for food will be less of a factor. I've seen a large (I think around 5000 L or so) tank in Belgium with a group of powder blue tangs. The pb's were already in a group for quite some time...
Time will tell, I'll keep my fingers crossed for you! This, together with Peter's topic is one of the topics I even check on my new iPhone when not at home