I stumbled into this totally by accident. I don't know if this applies to any other SACD player, but it happened with my Sony NS999ES. I sat down with my glass of vodka and put a CD on my surround sound. I was totally fine with the sound, but I noticed I was only playing my front speakers since my receiver was set to multichannel. I switch it to analog and PL2, and the seven speakers didn't sound half as good as the two from the multichannel inputs. Those S 412s never fail to amaze me. I stuck my vodka in the freezer and ran out to Radio Shack and got a couple of Y connectors. I split my front multichannel outputs to the multichannel inputs and the CD inputs. It was a hell of an upgrade for 8 bucks. I quit using the optical inputs a while ago since even the CD outs form this player sounded better, but this is an order of magnitude better still. I don't know how this will work out in another system, but for 8 bucks, you can't go wrong!
I just did the same thing with my DVD-A player and the same thing happened. This will work.