After reading this thread and many other reviews regarding these risers, I too went up to my local Guitar Center and picked up a Gramma pad. Was going to get the Great Gramma, but decided the Gramma would work fine for my PB-12NSD. As it is, it hangs over the edges ever so slightly, which works out perfect, now it gives my sub the appearance that it's "floating" almost.
The effects were immediately noticeable, even before I ran MCACC again. Low end is much tighter, bass sounds controlled and pure, and the really low Hz notes are heard better than before. No idea why I didn't do this a lot sooner!!
