I would actually put Small Bio Balls on top, Large Bio Balls, then Matrix, then Rings.
I'd also try to set-up a drip tray and have a pre-filter on top of the drip tray. Maybe a filter sock, or Filter Floss.
And the part about the bacteria is still out for debate IMHO, But it is Fact that Bio Balls work better in a trickle rather then submerged.
Mike