Sony STR-DA9000ES Operating Instructions Manual page 19

However, this large number of speakers may narrow the surround effect area. Thus, it may be more effective to set
"VIR.SPEAKERS" in the SURR SET UP menu to "OFF".
Please note that the front L/R and center speakers are common to all modes, and this function only changes the use
of the surround speakers. Depending on how you use SPEAKERS FRONT to switch the front speaker system (A/B),
and how you set "CENTER SP" in the SPEAKER SET UP menu ("YES" or "MIX"), you can set up two completely
different systems. For example, you can set up a 2 channel or 4 channel speaker system for pure audio sources, and
a 7.1 channel speaker system for AV sources.
Please note that in most cases you can use the 9.1 channel setting for Super Audio CD and other pure audio sources
without any adjustments. However, depending on the type of speakers you have and the way the music software was
recorded, you may want to switch to 7.1 channel or 5.1 channel playback. In such cases, you should set up your
surround speaker system to switch between A and B. Use surround speakers B for 5.1 channel operation and surround
speakers A+B for 9.1 channel operation.
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