Hi!
It depends on the cat - my boy was completely unaffected by Feliway (any of their varieties) although it appeared to me that it made him a bit uncomfortable. Comfort Zone causes him to leave the room. (I have found that Only Natural Pet's Just Relax works for him).
You could try cat music if you haven't Harp music has been shown to be quite effective in helping cats to be more calm.
I purchased their spray version - I haven't been on their site (Only Natural Pet) lately to see if they have diffusers . Thundershirt has a diffuser product you could look into too.