Two springs in series becomes a very complicated physics problem to solve (not unsolvable, but not easy). The solution can have higher peaks and valleys and some un-expected harmonics and singularities.
I think the Townsend springs will dominate but don't know enough about the Gaia to be sure.
Townsend podiums are actually engineered for their weight range rather than just guess what spring constant to use. So I would think you're better off with just the townshends.
Jerry