Late to the party here, but a few thoughts...
There are a number of ways to get audio data into Mobius. The easiest is to simply drag and drop files from a file browser (in your case Finder since you're on a Mac) onto one of the rectangles in the "loop stack" in each track. You can load up any number of loops in any of the tracks this way.
The older method is to first select a track (white box around it), then select a loop (white box in the loop stack), and use the File->Load Loop menu item. A file browser pops up where you can navigate to the file you want to load and it will be deposited in the selected loop.
I guess I should have started by clarifying what "samples" means in Mobius. If what you want to do is load pre-recorded audio content into Mobius where you can then play/manipulate them just like normally recorded loops, then you will want to use the menu items with "Loop" in their names.
There is an old feature called "Samples" that is still around but it was mostly used just for my testing, I don't think many people actually used it. This is what you see in the Configuration->Samples popup window and Configuration->Reload Samples. That is probably not what you want.
Using File->Load Loop or drag-and-drop will get the files in, but like recorded loops they will be lost when you use one of the Reset functions. If what you want is to have a collection of pre-recorded loops and backing tracks that is always there, that is one of the things Snapshots can be used for. I'll describe that if you're interested.