I'm not familiar with the Spec-S OSG but the OSG units i've run in 700whp+ Turbo NSX's and Nissan 350Zs (amongst others in stock powered NSXs, S2000, 350Zs, E46 M3s) were phenomenal.
I actually felt the there was too much preload in the off-the-shelf units (non-S) and deactivated plates and increased the spring rates of the negative internal springs and softened the preload washers, even in a 700whp Turbo NSX application. Here's the article on the OSG and how I tuned it:
http://www.motoiq.com/MagazineArticl...ferential.aspx
Sorry to hear you're having so much difficulties with them.