In your case it is, HDMI would be fine only if your receiver could handle DSD and your player could send DSD via HDMI.
Note on 2CH/MCH SACDs: on some hybrid SACDs, the MCH layer has more tracks than the 2CH layer. In these cases it makes sense to select MCH layer downmixed to 2 channels to be able to listen to the extra tracks on a 2 channel system. Example is Deep Purple 'Machine Head' SACD, 7 tracks on redbook and stereo SACD layers, 10 tracks on the MCH layer. So if you want to listen to 'When A Blind Man Cries' in hi-rez stereo, you have to downmix the MCH layer.
