I'm using an SDS steal...
Peter, do you mean you have and SDS Isoplatmat? If so, just plonk it on the platter first then put the original (thick) rubber mat on top - ditch the foam thing!

The Achromat is grippy, but not as much as the rubber mat. I'm also experimenting again at the moment with mats. In some ways the stock thick rubber mat (in conjunction with the SDS) is better than with the Achromat, giving a slightly less detailed but more coherent sound, and also losing a slight 'hard' quality in the midrange.

Marco.