There's a reason for that, my friend: you have two regulators in the line. Your hookup is a low pressure line, and does not need the regulator that is on the grill. Lose that one, and life will be good.
If you do a search here, there are numerous posts about how to do this. Note that some grills use the regulator to control the flame height. That type grill cannot be used this way. But as long as the flame regulation is done by a separate valve, and you can remove the regulator, you should be able to do this. It just requires some plumbing pieces.