In my setup, I only have two coax connections; and I have a 811 and a 510 connected to the same tv. So, coax out1 goes to a diplexer, and from the diplexer to sat in and antenna in of the 811; coax out2 goes to the 510. To my eyes, I see no degradation in signal strength or picture quality. I even the swapped cables on the satellite inputs of each receiver and still saw no difference in picture quality.
Hope this helps.