Just wanted to report back as I am able to test this without JAWS because it appears that Martin's suggestions are all Windows based shortcuts that I've simply never used.
If you are resting on a given file that is unselected, SHIFT itself acts as select. It does not, however, behave as a toggle since a subsequent hit of SHIFT on the file you've just selected does not unselect it. You have to hit CTRL+SHIFT to do that on the initial item you select.
If you keep SHIFT held down and continue arrowing (it can be up or down) each subsequent file is added to the collection of selected items.
Holding down CTRL and keeping it held down selects the first file you were on while leaving the files passed over unselected unless you hit SPACEBAR while CTRL is still held down, in which case the file currently rested upon is added to the collection of selected items.
One can also select a file somewhere in the middle with SHIFT, then while still holding down SHIFT hit the Home or Page Up button to select all files above it in the list back to the first. The same thing can be accomplished for all the files below it in the list down to the end by using End or Page Down in conjunction with the SHIFT key.
The only thing I can't yet figure out is how one might go about selecting a chunk of files out of the center as a block without using the SHIFT with either Up or Down arrow applied repeatedly.
At least this is somewhat easier than selecting text in a word processor or other text manipulation program!