Hi Finn,
Sorry about the delay in replying to this post.
We run a tracking back up system here and had the same problem with the avocent box.
As richard quite rightly points out we now use the easy sync box as you can specify the number of clients connecting to it, which is ideal as you want both the main and the back up to connect at the same time.
Just watch the pin out on the box as you will need a null modem cable to connect from it to the projector -anyway tell you how to suck eggs

hope that helps

Paul