OK, I've been through the 3805 manual. From what you have described, what I was trying to explain earlier is likely the solution. I wish I had explained it better.
Get to page 63 of the manual. In the right hand column, middle of the page is a section under the heading of "Input mode selection function". The first few lines expalin that when setting this to "Auto":
".... the types of signals being input to the digital and analog jacks for the selected input source are detected and .....the surround detector is selected automatically upon playback."
There are other modes to choose from, as you will see when you read the manual. If you move out of "Auto", which I believe you are doing when you fiddle with the remote, all of the automatic sensing and switching is compromised. Note that each push of the "Mode" button on the remote or receiver toggles to a new mode. Read pages 63 & 64 carefully.
Let me know how it turns out.
