I get along with Poser Magnets, well.  It took me a few years, with Poser, to get one to work; but as I'd feared, the only problem was elementrary.  

Anywho, yes a magnet can effect more than one part at a time.  When you create magnet set you do so with a specific part selected.  To add other parts, you you go to the Magnet Zone's Properties palette, where there is a Drop Down menu of all the other parts.