The biggest differences are these:
* DSD discs are 2 channel only and are home-brewed, i.e recorded from DSD-recorders or burnt from files
* DSD disc support is minimal, with PS3's, a couple of Sony SACD players, and a couple of laptops. There are also DSD plgins for a couple of sofwtare players
* SACD, although largely a protected format (now broken and available to be ripped as per my thread on it here) has slightly wider-spread support from several manufacturers (Oppo, Denon, Yamaha, Onkyo, etc), and allows for 2 channel and 5.1 surround.