Comment: In the first part

of his letter he defends the Fed by highlighting seemingly positive aspects, like remitting excess funds to Treasury. Here is how I'd reply:

The U.S. Constitution is the highest law of the land, and you swore an oath to uphold it when taking office. The Constitution says Congress is supposed to be responsible for monetary policy, not some independent third party it abdicates this responsibility to. So remitting any excess funds back to Treasury doesn't mean anything since that would happen anyway. The difference is when things go wrong economically the American people are told to look to the Fed, an entity they have no control over, rather than being able to directly hold Congress accountable including at the ballot box.

Why is that important? Because Congress, rather than pretend it could accurately set market interest rates which would result in the same bubbles and recessions we get now with the Fed, would not set rates at all but let the free market work, which is how it should be.

As for how much we can audit the Fed now, why is anything at all off limits? What needs to be secret? In reality, what we are allowed to see doesn't amount to much because the Fed can create and issue vast amounts of dollars with currency swaps and other unaccountable methods which the American people will never see, but can suffer by the inflation.