Hi Andrea,
Oh that's great news that the Moog Grandmother is 100% Eurorack compatible... didn't expect that.
Regarding mixers with panning options, I am using the Doepfer A-138p and A-138o combination and I am really happy with this mixer. The beauty of that is that you can expend it with another A-138p once you need more channels. Only space (and money) is an issue then :-)
Kind regards, Garfield.
For review reports of Eurorack modules, please refer to https://garfieldmodular.net/ for PDF formatted downloads