Volume should be 100% for soft-mixer & null-sinks when hard mixer is present, both hard & soft values should be saved
When testing out #698 setup (which has api.alsa.soft-mixer = true and 2 null-sinks) I've noticed that software volume for USB DAC and both null-sinks is not 100% even though I only use hardware slider to change it occasionally while digital signal is close to 0dB. Meaning that it was either result of leftover of some configuration or attempt of some logic to set it at "safe but loud" default.
I've always stipulated that software volume should always be used and exposed everywhere while hardware volume should be exposed only for direct user manipulation. But that implies that safe default for volume should be set only for hardware levels unless they are completely absent.
If it was result of auto-configuration then I suspect some of these changes: