@Miles-Thatch

This is what I found in Vegas 20.

Change an internal option: Rebuild peaks for visible events only: Change to TRUE

To get to internal options, you have to hold down the shift key while you select Options from the main menu. There will be an 'internal' option at the bottom of the menu that opens up. After the internal options opens, search for Peaks. You should see the preference for 'Rebuild peaks for visible events only'. You have to change the FALSE to TRUE. Then click Apply.

Restart Vegas to make sure the preference change takes effect.

Add enough audio tracks to the timeline to accommodate all the tracks in your media.

Minimize all tracks: Menu > View > Minimize All Tracks

Now, add your media to the project.

Note that Peaks will not be built.

Drag media to timeline with right mouse button held down, then drop. From a popup menu, select 'add across tracks'. Peaks will not be built. For certain audio, you can drag the audio tracks with the left button held down and then drop. The channels will be added across the tracks automatically.

Expand an audio track so it is no longer minimized. You could expand all tracks with Menu > View > Minimize All Tracks (to toggle off). Peaks will be built for the events on tracks that become unminimized.

While all the tracks are minimized (Menu > View > Minimize all tracks), you can select Menu > View > Rebuild audio peaks. All peaks will be erased for all media that is on the timeline because no events are visible. To build peaks for certain tracks, unminimize those track(s). The peaks will be rebuilt automatically.

If you open the folder that contains the media, you can see the .sfk files being deleted or rebuilt.

Okay. I think I got it mostly right.