Please remember that Ossynths systems are 'custom built' by Otto to suit individual requirements. I know Otto has built a system for someone to run three different locos (steam). you would need two separate systems, one for steam, one for IC, so could easily have two locos running at once. I know Otto is working on other clever additions, lights and smoke etc., being amongst them. His ingenuity never seems to falter, if you ask him for a feature not currently part of the system he will go away and think about it - and come up with a solution.
I'm not sure what Adrian means by 'engine notes sound weird'. Although electronically generated, they are faithful copies of real sounds. When I first ran the system in Norfolk, a friend came round to see the 'Lister stationary engine' he thought I had just started up!
Roy