The older stand alone extensions are not supported in DW CS6, the stand alone extension have been replaced by Design Extender and Data Bridge, these extensions are compatible with DW CS 6.
the design Extender and Data Bridge extensions also include some upgrades, a newer version of Pro Maps, and Data Assist.
if you contact the sales department, they can offer you substantial discount on those 2 since you already own super suite.
for eCart, you only need to download the eCart extension from the download center, then open the DW CS6 extension manager, click the install button, then select the eCart mxp file to begin installing it in DW CS6.