Hmm? Not an easy manual to understand, at least online anyway. If you go to page 60 of the manual, under "Control Area," "Controlling this unit," it appears there is a "multichannel button on the remote.
On page 30, "Basic Operation," item 4 - "Select the input source.," it seems to suggest that all you need do is push the "Multi CH In" button, and the multichannel inputs are selected, and you should be getting your hi rez audio.
All this, of course, presupposes that you, indeed,have a universal player, have it's 5.1 or 7.1 outputs properly connected to the receiver as shown on page 17, and are playing a DVD-A or SACD disc.