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I also found this interview which seems to support that speculation:
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This is a small sample size (just running around the immediate local area when starting a new game), but extrapolating from that small sample size I would expect there not to be much (any?) surround. I couldn't find any sounds that played in the rear speakers they are all positioned forward from the listener. In a strange coincidence I had someone ask about Diablo 2 and IndirectSound this week, and so I've been doing some tests in the opening level.
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