anode_______ground I believe this is exactly what you mean.
No that is not what I said please re read what I put.
And why don't you try the simplest possible setup (i.e. no reverse voltage) if you are having troubles?
You can always change it later if you do need the reverse voltage.
No if there is only a reverse diode across the analogue input then the input impedance is too high for the sample and hold on the input. You need an impedance of about 10k to prevent any apparent cross coupling in the multiplexer