Do differential i/p need to be clamped?

[Roff]

You are correct that the C cannot charge up due to the low resistance of the secondary winding that would always discharge it. This is a mistake on my part.

However any DC bias currents flowing in or out of the + or - amplifier inputs have no route to 0V. All of the protection diodes would be normally be off, apart from leakage currents, at the normal voltage levels at the + and - pins of the differential amplifier around about 0V.
The capacitor will provide some filtering of the transformer output signal and reduce the bandwidth at some point.

Mark, if you go back and read the entire thread (which I know is a pain), you will find that we have already beat the input bias current issue to a bloody pulp. And 100k resistors are much too large for this amp, which has bias currents on the order of 10uA. We already covered that issue too, but feel free to add to it, after you read the datasheet.
BTW, I used to work with a Mark Sanders, many years ago. I know it is a common name, so you're probably not him. I think it was in the Bay Area in California.