There are a few things you need to check. Verify that the Alesis is indeed outputting audio through the optical out, you will need to hook some headphones or the like out to the Korg to make sure that it is receiving the output from the Alesis. If it is indeed "hearing" it then the problem lies somewhere on the Korg side. The most likely scenario is that the input is selected incorrectly on the Korg, make sure you have the Korg looking at the optical in, as there are many inputs on that device I'd say most likely the correct one is simply not selected for recording.

So to verify, make sure audio is coming out of the Alesis across the optical cable, then make sure the input selected on the Korg is that optical cable (I'm pretty sure there is not a seperate selection for recording, so as long as you're on the right input it should record whatever you hear.

Hope this helps, sounds like the problem may be as simple as the input being chose incorrectly on the Korg side, but make sure you really do have audio coming from the Alesis on the channel you want.

Good morning. Have you checked your output settings on the source equipment and the input settings on the recorder? You may have to designate those manually.