The syno wil go soon. The synos have shared the tanks with my tigers fish for over 4 years now. Some small fish if grown up together ... Can live no probs with monsterfish.
My main concern is the ray trying to kill them for fun or even worse damage itself if it tries to swallow the small cat.
WOW i missed this thread, just read up on it all and i have to say its smashing. Great fish, Great set up & i would love to see some nice rays in there