(C) request the testimony of, and production of any document in the possession of, any other person, including any client of a registered public accounting firm that the Board considers relevant or material to an investigation under this section, with appropriate notice, subject to the needs of the investigation, as permitted under the rules of the Board;
(D) provide for procedures to seek issuance by the Commission, in a manner established by the Commission, of a subpoena to require the testimony of, and production of any document in the possession of, any person, including any client of a registered public accounting firm, that the Board considers relevant or material to an investigation under this section