The 36 mm festool hose, which has a slightly flexible hose-end won't fit the atf 55.
There is a reducing sleeve with partnumber 768135 (which I cannot find on the festoolusa site, but it might be possible to order anyway)
link
It has the tool-end of the 27mm hose and fits inside the tool-end of a 36 mm hose, it might be compatible with other hoses aswell.
The standard festool hoses will work without modification with a lot of other vacs aswell, for instance, I have a hitachi and a spit(starmix) vac, to which their standard hoses attach with a bajonet-type lock to the vac, but the festool hose fits inside the hose-attachment to the vac no problem.
There's also a non AS (anti-static) version available of the hose, wich has the same tool-end, but is a bit less expensive.
Link (The 3.5 m is the standard length, and matches the powercord length)