I have been trying to use Max 6 for a few months but finally had to give up and go back to Max 5 as I was getting too many intermittent crashes that are not understood.
I'm very grateful that the patchers are all backward compatible and everything I built with 6.x loads just fine into 5.x
However, I found that when I tried to reload fxp files in Max 5 that had been created with Max 6, the VSTs were not configured. It's not a huge deal because I was able to just save the VSTs patches themselves and then pull them back in.
But I'm curious as to why that doesn't work. The VSTs are identical, there aren't extra (or fewer) parameters in them. So what is Max6 doing when it saves an FXP file that is confusing Max5