I know this is probably a newbie question but can C Studio 5 and C9 Pro be launched simultaneously on the same computer?
It should work. But did you consider just trying it to discover for yourself. 
Thanks for the reply but no because I’m in the middle of a project on one and didn’t want to freeze anything up if it wasn’t permissible.
At this point it would be easier to ask.
Yes, but make sure they don’t use the same ASIO drivers.
Otherwise, if you want both to use ASIO, there’s this: Support for using ASIO with multiple programs at once - PG Music Forums (which I haven’t tried myself)
Thanks DJW!
I’ve never had a problem with using the same ASIO drivers with multiple versions - everything worked as expected.
We’re talking about running those two versions at the exact same time. If they both try to access the same device through the same ASIO driver then it won’t work unless you have some special setup.
Curses upon you djw. You forced me to go into the other room and boot my DAW before I’ve even had coffee. 
So I just had C9 and C8.5 playing different projects at the same time. It all worked fine (ignoring the resulting cacophony of course).
Nothing special setup here either.
Sounds like you need to move your source of coffee closer to your bed!
Are you sure they’re using the same ASIO driver? By default, it will probably try to select an alternative in one of the two instances.
If I try to do what you say with the Yamaha Steinberg USB ASIO driver, I get this on the second program:
I only have one ASIO driver. Maybe RME designed their driver to accommodate concurrent use.
In Device Setup/VST Audio System, I do have Release Driver When Application is in Background unchecked.
I think it’s rare, but I guess you have a multi-client ASIO driver. It’s beyond my expertise since I’m not fortunate enough to have hardware like that. 
Yes…RME drivers are multi client. Most aren’t.
Cool. Thanks for the info.