With digital output set to "raw" the speaker setup page settings don't really matter because the 970HD does not perform any audio processing. If you were using the multichannel analog output, I'd recommend "downmix" to "5.1 CH," the speaker sizes to "large," the sub to "on," the distances to "0," and leave the channel trims set to "0db" because the 990 will apply necessary settings to the multichannel analog input - but with just the optical connected, none of it matters.