3 ideas come to mind:
1- You could try the dialog normalization parameter with your DD playback DSP. Maybe make a duplicate preset so you can have one for TV and one for other inputs. You could increase the playback volume to match the DPL?
2- You could tell your Tivo to not playback DD at all- everything would come out as 2.0.
3- You could use the analog outputs- this is really another way of #2 if the Tivo won't allow you to convert everything to 2.0.
Actually here is #4- use analog output for normal TV viewing, but also run the optical into the 861 for the times you want 5.1. Now you have both
