At the same page where the Dark Sun Campaign Setting recommends the use of the Fixed Enhancement Bonus rules, it also suggests a reduction on the number of magic items awarded. It suggests you should remove parcel 1 and 4 (which are the least and most powerful magic items) of the treasure given per level. This way, at each level, the party would receive about 2 magic items. The book also says you could replace one of them for a Boon or something nonphysical but with magic effects once in a while.
But for some people even then there would be too many magic items for Athas. For others it’s too few treasure to give to their players. An option, which I have been designing, is to give fantastic items suited to the world of Dark Sun that have magic proprieties similar to magic items, but that are not traditional magic items as we know it. They could be handed out in the place of the removed parcels or even as the remaining parcels to reflect how rare magic items on Athas are.