Yamaha MTX Series Setup Manual page 49

Example 2) High audio quality system with XMV and YDIF connections (digital connections)
Up to this point, you made separate settings for zone 1 and zone 2. However in some cases, such as a party, you might
want to remove the boundary between zone 1 and zone 2 so that they can be a single meeting area. In this case, make
settings in the "ROUTER" screen to route zone 1 to output 2, so that zone 1 and zone 2 can be used as a single space.
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MTX Setup Manual