I tried to find a solution to this for one of my customers, but had no success, however I am no expert on monitor inputs. I tried getting a CRT computer monitor that had both VGA inputs and the same signal split to RGB but the S5 seemed to be missing a sync signal that the monitor needed. I also tried an RGB to VGA converter that was meant to allow old Apple MACs to work with standard screens, but again no joy. Fortunately the problem went away as they finally upgraded that part of the plant to S7s.
I did find that RGB monitors were usually repairable at my local TV repair shop, but they went bust after everyone started switching to LCD televisions.
Bryan