Sorry for the delayed response - my PC died an unexpected software failure that took me a while to recover from. I just tried a test similar to the one Steve mentioned, using a 2 channel SACD disc, with the SACD player set 2 channel config set to "two + sub", and verified that I was getting a sub signal through the 6 channel direct sub input. (I disconnected the two main channels to make sure that the sound from the sub was not any bass redirected by the 950.) So, as Steve pointed out, the quirk appears to be with the volume level of the sub test tone from the Sony, not the 950. Thanks for the help.