I would suggest go to down, it has way more to do than sitting in lounge for 7 hrs
you dont really need to leave the airport express line at all, all the stations are a shopping complex itself once you exit the gate. The ones at kowloon station and Hong Kong station has more variety of shops than Tsing Yi(more for people living in that area, since it is the only place they can shop without leaving the island). Is call Elements and IFC if you want to know the name.