First, the 800 is a player, although it might function as a preamp/controller with the right board but without the flexibility of the 861 or of any topline preamp.
Second, the 861 is a digital device and all analog inputs are digitized for processing before D/A for output. The various versions differ in the sophistication of the DSP operations but the sound quality is more dependant on the input/output cards. For example, there are now 24/192 analog inputs but older 861s may have A/D of lesser resolution which may or may not be subjectively significant. So, you should find out exactly what you were listening to.
Finally, the latest 861s, version 4, have room EQ ability and that could have been a real factor in auditions.
So, no easy answers but I loved the older version and have just had mine updated to v4 and 24/192 input!
Kal