They also will attach to the MFT/3, directly to the aluminum extrusion that is the outer frame, ("profiles" in Festool lingo). The MFT/3 is the same height, (900mm), as the Kapex on the UG stand or on the MFT/3 Kapex.
The MFT/3 Kapex, is shorter so that when the Kapex is sitting on it, the MFT/3, CMS, folded up UG stand handle are all at the same height as the Kapex work platform/turntable. It's a system - and 900mm is the magic number...
Tom