Bart, my reluctance to wade through a player manual was mooted by varkha doing all the hard work. In looking at p.38, as he indicated, there're two settings that have to be changed from the 2-channel default: the selection of the multi-channel track on the SACD(which you say that you did); the selection of the 5.1 channel audio output(which you haven't mentioned). Unless you did it but just didn't mention doing so, it appears that varkha has uncovered the problem.

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Enjoy the music, not the equipment.