I think you have a white balance issue with your originals, as well as a bit of an issue with underexposure. The post processing corrections lschaff did on your samples in post #8 is more the direction I think you need to go. Honestly, for outdoor,daylight flash fill-in using something as low-powered as an SB 800 with a Nikon camera that has a baseline ISO of 200, I think that bouncing your speedlight (roughly a 60-watt-second flash in terms of a Speedotron studio strobe) I think you are wasting your time,and yor speedlight's limited output, by bouncing the flash off of a bounce board or an umbrella. Many beginners think they need to soften-up fill-flash outdoors. Not so, really, just not needed. Your main light in all these is the sun, a point light source; your fill in can also be a point source,and it will look great if you just get the balance of ambient to daylight right.
Outdoors, fill-flash that is shot even directly on-axis, right on the camera's hotshoe, can be mae to look pretty good if you get the right balance between the ambient light exposure and the speedlight's flash output. The problem really lies with bright sunlight, and Nikon bodies that have an ISO 200 base ISO and a maximum flash synch speed of 1/200 second; your "basic sunny sixteen rule" means you are stuck at 1/200 second at ISO 200 at f/16 or thereabouts. Regardless, with "most" Nikon d-slrs except the D70 and D40 series that can synch flash with daylight up to very high speeds, you are STUCK using a top shuter speed of 1/200 second AND a small f/stop like f/11 to f/16, and at THAT small of an f/stop, your SB 800 has very little range or power, and even LESS rang and power when you bounce its output off of a foam-core or other refelctor surface.
The base ISO of 200 is a limitation of many Nikons, and one area where Canon's original 5D with a baseline ISO of 50 proves its worth for more flexibility outdoors,allowing you to use larger apertures for more shallow Depth of Field, and simply more choices in terms of ISO/flash/f-stop combos when doing outdoor fill-flash work.
I think you have the right idea with your Nikon--to shoot with the sun back behind the subjects, or sidelighting the subjects somewhat and using flash to fill-in and brighten the shaded side, but you really need to get the flash power UP, higher, and the easiest way to do it would be to get rid of the flash bounce board, and go to straight, undiffused, bare flash which will look perfectly FINE outdoors.