Here's a calculator I found online.
Woodweb It just gives board feet though, not in a 2x6 shape. For a 16" by 8' log it says you'd get 72 board feet which would be 9 2x6's. But that is assuming 1" thick boards so they fit nicer into a round log shape. So I'd guess that you can probably get 7 2x6's from a log that size. That's just a guess on my part not based on experience.
To get a more precise answer from the experts out here, you may want to specify the log diameters and lengths. I'm not sure which the (16) is referring to...