Or you can use Badia LiveKeys Xtension: it lets you totally customize keyboard shortcuts in Xpress and add new shortcuts to items that don't have one.
Lite version is FREE!
http://www.badiaxt.com/products/livekeys.html
Anyway, you don't need to turn on full res preview one box by one. You can select all boxes on the spread and turn it on or off all at once.
Andrea Calvetti
Florence, Italy
QXP 9.2 - Mac OS X 10.7.2