1. Direct from scanner

Signal generator is set to 30 mVpp on 146.420 MHz into a dummy load. Scope is clipped to 3.5-mm extension cable tip and shank, probe on 1:1. Looks like a good solid signal coming out of the scanner around 560 mVpp:

Boosted signal up to 60 mVpp, scanner out jumped to 680 mVpp:

2. Sidekick board measurements

Turns out the schematic I have is for the old version of the sidekick board the one without the aux jack. So it's really TP5 I need to be measuring. Here's 60 mVpp on TP5:

The sidekick appears to be loading down the scanner output quite a bit. Also of note, that's with the gain trimmer all the way CW. If I turn it back to about midrange, i.e., where it's supposed to be, it's only around 230 mVpp.

3. Baofeng vs. Scanner

Turns out not to make any sense to do this -- the Baofeng's output into the dock is variable with the volume control, so you can drive whatever the input is to the 800 mVpp target.