Aha! There it is. 4 dB of pre-gain. Thank you!
Lesson learned: Don’t hide the Pre rack when there’s non-zero values in it. Otherwise, don’t store non-zero pre-gain settings in Track Archives, where they’ll sneak back into your projects unnoticed.
But, that’s not the whole story, it turns out…
I was still hearing distortion when, for example, the clip volume was raised by +10 dB while the channel fader was reduced by -20 dB (for a net reduction of -10 dB). Distortion at -10 dB? With 64-bit floating point? Weird. And, this too: Channel level (and all meters downstream) were topping out at -20 dB, rather than -10 dB. Clearly, something was hitting a ceiling and clipping in the channel strip.
Well, when I said there were no inserts on the audio track, I should’ve said, “no enabled inserts.” In fact, there were four inserts on the channel, but the insert section was bypassed. When I removed the Waves MaxxBass plugin from the channel, the distortion disappeared and the peak levels returned to -10 dB. Likewise, when I merely deactivated the plugin (as opposed to bypassing), the distortion disappeared.
So, Waves’ MaxxBass v188.8.131.52 has some issues, even when bypassed. All version 9 Waves plugins are supposed to be 64-bit compatible and, if I remember correctly, worked fine in prior versions of Cubase.
Thank you for the spot-on recommendations! It is very much appreciated.