Nope, not a good choice. #6 is a "cleaner wax" and is best used as a stand-alone product, or as a first product to be followed by another wax rather than by a polymer. #20 contains solvents that are intended to strip contaminants (like previous waxes) so that the #20 will stick to the paint better. So, you can do it, but it would be "wasting" the #6.
And you can't do #20 followed by #6 because the cleaners in #6 will remove the #20. Then you would be wasting the #20.
You should put on the #20 first. Then, if you want to put a wax on, if Meguiar's use #26 liquid or paste, or #16, or you could use S100, P21S, or Pinnacle Souveran (liquid or paste), or Collinite, or any other non-cleaner wax.
#20 will look really nice on white, btw. It's very reflective.
Tom