Soundsource 5.3.8 Here

SoundSource 6.0. 0Paid Upgrade From SoundSource 5 or SoundSource 4 * Send Any Audio to Multiple Devices, With Output Groups. ... * Rogue Amoeba

This version family provides comprehensive control over your Mac's audio that goes far beyond the built-in system settings: SoundSource 5.3.8

If you are currently using an older version or are new to the software, here is how to set it up: SoundSource Release Notes - Rogue Amoeba SoundSource 6