"Hybrid" refers to the fact that the disc has two layers, one reflects light at the wavelength of a CD player laser, and the other at the wavelength of a SACD player. Of course, the CD layer, which you can select, is 2-channel. On the SACD layer, there is both a stereo, and a multichannel recording, which the user selects.
DVD-A are multichannel, but can also be played in stereo. In this case the player does the mixdown as the disc is played instead of the recording engineer doing it when the disc is produced. I think this is a better approach because no data space on the disc is wasted by a duplicate recording, and details of the mixdown can be selected by the user so as to give a different sonic perspective: on stage with the performers, or out in the hall.