Will,
have you installed the rear sway bar with the Standard suspension or together with the SSL-coilovers? If with standard, was the sway bar connection enough to stiffen the rear? The Plus Six is so soft in the rear that both sides in parallel travel a lot over ondulations and in faster corners, while the suspension moves through its travel, the whole rear also moves sideways, maybe because of the geometry.
I've ordered the Librands kit now and will report once it is installed.
Markus