Interesting, with the analogue outs for SACD, did you set the Oppo to DSD rather PCM. If not, the conversion would be DSD to PCM before being converted to analogue, effectively the same as HDMI albeit that the type of analogue cables would affect the sound more than HDMI.
I can't find it now, but there was a quite a bit of technical info on it on another site (not that one) relating to the Oppo. If the Oppo has to convert DSD to PCM because the AV amp doesn't accept DSD via HDMI, the sound is comprimised. The deduction was to set the analogues on the Oppo to DSD and thereby cut out the PCM conversion. Guess I'll find out for myself tomorrow!