You keep the current shares in ISX - which at the moment are...

You keep the current shares in ISX - which at the moment are trapped & you then get given 1 share in ISXFEU for every share of ISX that you own.
Keep in mind that if these were both trading / listed entities at the time of the demerger it would be an awesome thing, however at this stage youll just end up with your existing non tradable shares & new non tradeable shares in a Euro entity. Until such time that they manage to list on an exchange the euro entity, & or get the ASX entity relisted.