Example: You record a family party. The AVCHD recording quickly sums up to some 00080.MTS. You start your new project only with a subset of all clips in the STREAM folder. Let PrE9 choose its best match preset for project settings, Accept it and use it for the rest of the clips in your STREAM folder of that family party recording.
I may have misunderstood zimmedl+1's problem, though.
I just was going to add a quote from your important advice from "Can't view video":
Steve Grisetti wrote:...The best indicator is to place your clips on the timeline. If you don't see any red lines above your clips on the timeline, you've got an ideal match between source video and project settings...