Hi Callum,
The answer may be closer than you think,
Something like the Medialon Showmaster LE is perfect for this type of thing as it can even take MIDI In , it has drivers built in to control Watchout , PJ Link etc and has a time line
Its a 1 RU Box that has a Web Server Interface or its own Panel Software that can run on up to 3 separate devices on the network, Its quite easy to program and Medialon and Watchout have been used together in dozens if not more High end Musicals and theatre shows World Wide since the early versions of Watchout
so the combination has a Great Track Record
If you want more info give me a call
+61 2 94363022
Dean
Interactive Controls
Sydney Australia