I may be speaking out of turn, but working with megatons of disparate media in the TV industry [stills/audio/video], I found that media sitting on the desktop provides the easiest, fastest, and most stable access to said media. Transferring this ideology to Poser 13, I just create a Runtime folder there for all of my content. It looks a little weird in the Poser's GUI library, but works really well [this concept should work equally well in PC or Mac].