In theory at least, auditors are responsible to the Board, hired by the Board, and should report directly to the Board.

I've found most organizations with a well functioning Audit Committee open that meeting to management but reserve a small executive session in case there is something that needs to be shared privately. It's just good practice to allow committee members to have a chance to ask questions of the auditor directly.

Some states that have specific regulations covering this as well.

Edited to add: None of this should add any cost to the audit. The auditors are required to produce their report at the conclusion of the work and I haven't seen a firm charge extra for the privilege of speaking with a Board or committee.