When I had Bob work on my RF-3 XO's, I had seen that thread too. The guy was not listening to anything that any of the members were saying, and instead just stopped reading when there was the slightest bit of criticism - no matter how constructive (or lack thereof). I opted to have Bob build mine. He built them on wood, which looked very nice, and seemed to work very well. I then installed the XO's in the front of the tower underneath the lower woofer. I trimmed the foam just a little bit; enough to make room for the components on the board. There were no issues. As long as you're leaving the foam around the port you shouldn't have a problem.
I would imagine that the 5's should respond well to an XO update. My 3's did, to my ears anyway. I also swapped out the tweeter diaphragms, but I'm not sure you'd want/need to do this in the 5's.