Sorry I can't be of any help, but I have a CSPPC (by Phase5) plus G-Rex + Voodoo 3 3000 etc and WHDLoad games and AGA demos work as well as ever.
However, you say that you have tried changing waitstates etc. My CSPPC may be an earlier hardware revision that didn't allow modification of these settings as they are greyed out. I wonder if anyone else that has these settings available has trouble with G-Rex and AGA apps.
Does your 2nd CSPPC allow waitstate settings changes?
