Sorry to throw a spanner in your plans but I actually ordered the X light after all the discussions above and they're not 100 percent hollow. I could not get a cable through from one side to the other. I could get water to pass through the bars but cables got blocked / stuck so there must be some lattice or internal support that was making it too hard to get a cable past. I've just had to return them. They're ridiculously light though so would make great bars for a non di2 build.
Sorry to throw a spanner in your plans but I actually ordered the X light after all the discussions above and they're not 100 percent hollow. I could not get a cable through from one side to the other. I could get water to pass through the bars but cables got blocked / stuck so there must be some lattice or internal support that was making it too hard to get a cable past. I've just had to return them. They're ridiculously light though so would make great bars for a non di2 build.