Ok, update.
I've given your idea of using extenders some thought, and you're right: it would be easier to use extenders and keep the electronics in one centralised server area. This way it should be a lot easier for me if I wanted to upgrade the motherboards in the future. (I wouldn’t have to remove the panels every time, avoiding the risk of damaging the plaster on my walls)
I’m quite lucky in fact. For one panel I don’t even need an extender since I will be able to put the cables throught the wall (the server room is literaly behind the wall where that panel will come). This also has the advantage that, instead of having difficulties to mount the panel in a self-chisled alcove in the wall, I can actually make a hole in the wall and secure the panels from behind. The other panel upstairs will be built into a false wall, and will also be easily accessible from behind. I intend to get to the panel using
RapidRun cables. (I stole that idea from Oliver in
this post - I only hope it won't be too difficult to find them in Europe).
I think the bigger panels support DVI, I've got a 19 inch one that does.
I immediately believe you when you say this, but 19" is just a *tad* too big to install inside a wall.