The manufacturer of the tub has nothing to do with the drain. I cannot understand your explanation of what you have now, but there is no way that you should have to "rerun all new plumbing back to the main drain". And I cannot imagine any competent person tell you how far you would have to redo your plumbing without seeing your individual situation.
I believe that this is turning into more than it needs to be. I cannot imagine it being such a major ordeal to put a different trap in if you have access. It may be time to call a plumber.