I'll let others answer the amplification question. I think the big thing that would make me consider the 805 over the 605 is the extra HDMI input (3 versus 2). I'm actually going for a unit with 4 inputs. 2 wouldn't be enough for me. I use the PS3 for SACD/Blu-ray playback, the Toshiba HD-A1 for HD DVDs, and I also have an Oppo for DVD-Audio. When I get a new Xbox 360, it will have HDMI, too. So there go all of my HDMI inputs. If you can't foresee needing more than 2 inputs, then yeah, the 605 would probably be enough.
