Actually, the only way you can play 2-channel discs from the front left/right 5.1 outputs is if you play around with the MCH management settings. This is directly from the manual:
"Playback mode - 2CH + SW*
* The audio signal is output from the ANALOG 5.1CH Front L/R jacks and no signal is...
Owning the XA777ES and other SACD players from SONY - I can tell you that the XA777ES is set to run when your remote is set to CD1.
And as mentioned, you cannot change this setting with the XA777ES - therefore you are "forced" to set any other SONY CD/SACD player in your system to CD2.
I...