Listener57, yes use them upside down. It make no difference in the performance of the Aurios. If you want tungsten carbide balls, which I strongly recommend, I know of nowhere cheaper than McMasters/Carr, at least if you can get them at wholesale prices there. This usually means buying them in quantity. I bought 56 balls.
Mitchb, the ProAurios and the newer Aurios have a large depression or hole where larger balls will not so easily come out. I do find, however, that the old 1.0s outperform the newer Aurios as the race depression is shallower. This means they are very sensitive to a level surface and that they are freer to move if need be. You can with a level surface use the balls, but you have to be very careful. If you can, remove the unit place the Aurios with balls and carefully lower the unit into place.
I have not tried it yet but since the balls don't move, you might superglue them into place.