Jumping in here as well - same problem, followed the directions, watched the video, only detects one tower. Possibly something a bit weirder going on as the secondary tower flickers around a fair bit before I plug the main tower into the PC, whereupon it goes static; usually no light on the tower save for one red or green light on the last LED down the bottom.
Have updated all firmware + iCue, and the main tower works fine and is totally responsive to iCue. For whatever reason though, the second one though isn't playing cricket.