Is SoundID output volume lower?

Yes, the output volume is lowered for audio quality purposes

One of the main reasons -  you should have as little compression as possible, but we're also concerned that sound processing will introduce quality loss (clipping, sound artifacts, etc). In order to provide a signature experience while using SoundID, we are using smart technology to improve your audio listening and bring it to the next level.

With this being said, we are looking into future updates, that should improve your audio listening experience even further! Yes - we will try to improve upon volume output, so it's not as visible without making any compromises on end-quality.