How can I set a max/min limit for the OSC signal sent by AnalysisGrabber?

Welcome to the forum crixxx!

There is currently no way within the plugins to limit the output to a different range than the range of the mapped parameter.

The Group option is a different type of feature; it determines how the grabbers behave if you have multiple parameters mapped to the same OSC address. More info can be found in the manual: Free Tools Support | Showsync

Typically for more processing of the OSC you can rely on external tools like OSCulator.