Well I tried some of these demos on my STE 4 MB with TOS 1.62.
Braindamage and Antiques do not work with CosmosEx. However they work pretty well with HxC Floppy Emulator.
I didn't know there is a HDD version of C++ is forbidden, but the floppy version is ok.
Concerning HDD demos I don't think the problem come from CosmosEx. Isn't it a TOS version incompatibility?
Strange Robots work well. Did you tried other Blabla demos such as Circus back²STage? (http://www.pouet.net/prod.php?which=61178