This is an attenuverters module in Kosmo format. It uses some ideas from the Kassutronics Quad Attenuverter / Mixer.

There are three attenuverters. One has a switch to select 10 V input instead of the input jack. (I did it this way rather than normalling the jack in order to make sure 10 V is not sent to the sum unless it’s really wanted.) There are jacks for output of the sum and inverted sum of the three channels. Response to slider position is nonlinear, giving you finer control near the middle for setting small values.

Schematics, KiCad design files, Gerbers, docs here: