I just checked my setup and unfortunately you will need at least the front display to setup multi channel on the 805. You have to assign an input button to use it. In my case I used the vcr button and had a SACD/DVD-A player connected to the multi inputs. If you were using the multi channel inputs before then you would be able to use that input button again and use audio sel to activate. If not then it would be some trial and error to turn it on. If you like I could go through the button sequence that would turn it on for the DVD input button. Although you will also want to set your 805's volume control to come on at a set volume at start up. Again just another sequence of button pushes. But it's set point would have to be a guess. A working display would be much easier of course
The fix for the display is here http://www.avsforum.com/t/857502/the-onkyo-tx-sr805-thread/17300_100#post_15249416
it would be a very easy fix, even if you only have moderate soldering skills. Although some people have tried it and it still didn't work, several other have had success.