From the http://www.floridamusicco.com/proddetail%7Eprod%7Ecustom_and_vintage_sdx.htm

‘Important! Please Note:  If you choose the download option, we can only accept Paypal payments from a confirmed and verified Paypal account.  EZ Drummer and the EZX expansion packs can be downloaded in their entirety from Toontrack’s website.  The Superior Drummer 2.0 and SDX expansion packs can be partially downloaded from Toontrack, but a separate Installer Disc is necessary for the complete installation.  If you already have an Installer Disc, choose the ‘Download no disc’ option.  If you do not have an Installer Disc, choose the ‘Download with disc’ option.  Shipping charges may apply for the ‘Download with disc’ option.’

So if you have the VSSD installer box (the ‘black box’) with all of the Toontrack products, then you don’t need the installer discs (obviously, since you already have them). But, if you do have a VSSD box, make sure you have the disc(s) for the product you want because as new products get released, you may or may not have the installer discs for the product you want.