I checked and double-checked my settings.
Unfortunately, I still get only two channels being input to my Yamaha 5990, just like when watching SD from the cable box.
When watching HD channels (via HDMI), the receiver's input indicator shows LFE, L, C, R, SL, SR, 5.1 separate channels.
When watching the 85H (also via HDMI), all that lights up is L and R. The receiver decodes it into surround sound, but the DVD I was playing was in 5.1 (THE EMPIRE STRIKES BACK SE).
I may reset the 85H to its "fresh out of the box" setting and trying again.