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...
"Hundreds of years from now it will not matter what my bank account was, the sort of house I lived in or the type of car I drove... But the world may be different because I did something so bafflingly crazy that it becomes a tourist destination"
I think the length of the logs has an effect on how much you can get out of them, too. 16' logs if they have any bend at all will be less effective at converting to 16' 2x6s than the same size of 8' long logs to 8' 2x6s.
Also, if you want only 2x6s, you will lose some timber volume that could have made a 2x8 or a 2x4.
From a graphed sketch, it looks like you could get up to 14 2x6 (full dimension rough) boards from a 16" diameter log. In a real log, you would probably get some wane in one or more of those due to logs not being mathematically perfect cylinders.