Nice install job, Mike!
I don't recognise that sound module you've used - you said it was an old one, but I thought that the Massoth S was always the little tiny board (about 35mm x 20mm, and without screw terminals) right from its first release - what you've used looks much larger?
Just curious, as it's a Massoth item I've not seen before.... was it something short-lived, that was released before the current S unit?
Jon.