Thanks for pointing me towards SideCar! I think this might actually be exactly what I was looking for. I want to mix some of my Eurorack audio signals before they go into the ES-9, mainly so I can make better use of the available inputs for parallel multitrack recording.
This module seems to make much more sense for this particular purpose. I hadn't considered it at all, so this is a really useful suggestion.
The only thing is, I am missing one more stereo channel :-D .. 2 Stereo Channels are good, and 4 Mono Channels. But I need one more Stereo channel. So I could use a Ladik U-081 Fader together with a Divkid Stereo Strip XD