I'd guess you only have two options.
1. Use the Mixer.
2. Use the F5 key and set the volume for the Piano there


Boyd
Win10 - 16GB-RAM - BiaB 2019 - Mixbus 4 - Slate Bundle - Komplete 10 - Ozone 8 - Neutron 2 - Waves Gold
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Sonarworks Reference 4 -