Module is available as a DIY project only.
No info about availability.
3-channel bipolar mixer/attenuator with 5V offset
Grayscale panel for the RYO Vertmix:
http://grayscale.info/panels/roll-your-own-ryo-vertmix/
Vertmix was designed as a handy CV mixer and processor with buffered inputs but its low-noise circuit means it will also work great with audio.
A 5V offset is normaled to the input of the first channel, giving it a maximum of 5V out turned full clockwise/right or minimum of -5V turned fully counter-clockwise/left. Please note that this offset will affect the mixing if the channel hasn't been patched on its input or output.
It works as 3 channel bipolar mixer,
1 bipolar attenuator + 2 channel bipolar mixer
or 3 bipolar attenuators.
The buffered inputs offer very large resistorless jFET impedance and is unaffected by output impedance (isolation/protection resistors) on the modules going in to the mixer. The inputs without offset voltage is grounded if no patch cable are inserted. If a patch cable is inserted in an input but loose at the other end, the input will be floating (this is modifiable by a resistor between input pin and ground on the input jacks, input impedance will then be equal to this resistors value).
The outputs have 1kohm impedance.
These merchants probably sell this module. Huh?