On the CS-80V, there's a midi channel parsing in Multi mode.
When using a multi preset, you can choose a specific midi channel in the right part of the multi page for each of the 4 zones defined.
Some of the "Factory" presets may have some zones not configured on "Omni" mode (to allow any Midi Channel to trigger zones). Depending on the Midi Channel currently used with your controller, if the appropriate Midi Channel isn't properly defined, no sound will be produced (even if you see the virtual keys being pressed):
Just make sure to select 'omni' in the Midi channel section for all the zones currently defined in the "Zone" section and it should work fine from there.