Those expansion devices over I2C will not be much good at all for analog signals. They are really suitable for low speed digital IO. There are SPI versions of these devices available that can obviously increase the update bandwidth...
Oh my god... Thank you so much you two. I feel really dumb for making such a mistake!
I cant believe it was something so simple.
I was searching for this for ages and couldnt find the sollution. I was almost sure, that I had a...
FWIW, you can operate CAN over very short distances without transceivers.
It is absolutely critical that you use a 3.3v source instead of the 5v shown!