Good news, I've finally got a solution. Sierra knows about the Corsair Strafe RGB now, however, if you've ever installed ckb to get the lights working, then ckb-daemon interferes with the modifier keys in some way.
Here's the check and fix:
1. Confirm this is the problem: check for the process "ps ax|grep ckb-daemon" (no quotes) if it's the issue, you'll see ckb-daemon running. If it's not, don't bother with the rest of these instructions, this isn't the solution you're looking for.
2. Delete ckb from Applications: open a Finder window, click on Applications, find ckb, and trash it
3. Kill ckb-daemon: either restart your mac or execute "sudo killall ckb-daemon" in a shell
4. Confirm it's no longer running by checking for the process again: "ps ax|grep ckb-daemon" you should only get one line back showing the command you ran
I hope this helps those frustrated by this. Unfortunately this fix loses any cool lighting features of the Corsair keyboards, leaving it only backlit by white.