Parameterizing the whole project?

quote]I was thinking about using project variables, but the question now is how can I execute/loop the whole project 6 times, each time with different combinations of these variables.[/quote]

If you run TestComplete via the command line, run it six times, each time passing the needed values as command-line arguments. In the test that runs first, you can analyze the command-line arguments with the ParamCount property and the BuiltIn.ParamStr method and assign the appropriate values to the project variables.

Alternatively, create a keyword test or script routine that will call all the other tests and run this test (script) as many times as you need.