Not sure it has those specific features but you may want to check out Sound Control. Source: 11 months ago

SoundControl is exactly this and more: https://staticz.com/soundcontrol/. Source: about 1 year ago

Hey, bro, I think I've found a solution: I installed the SoundControl software, enabled the "Force Soft Volume Control" option. Yay, the volume is now adjustable! Hope this helps you too! Screenshot. Source: about 1 year ago

I haven’t installed it yet, I’ve got a few days off and don’t want to waste the trial period. This is the one I bookmarked from the ones I found: https://staticz.com/soundcontrol/. Source: about 1 year ago

IDK whether a 3rd party software audio mixer would help; you may download a trial here: https://staticz.com/soundcontrol/. Source: over 1 year ago

Found this article which suggests Mac Media Key Forwarder or BeardedSpice. Source: about 1 year ago

If you're on macOS, BeardedSpice should work: https://beardedspice.github.io/. Source: over 1 year ago

Use beardedspice to map the multimedia keys: https://beardedspice.github.io on the K3. Source: about 2 years ago

I think https://beardedspice.github.io used to do this but it hasn't been updated since 2017 and doesn't work properly for me. Source: over 2 years ago

BeardedSpice lets you bind them to a specific player. Source: over 2 years ago