Half of lawyering is reading and comprehension. Now...
Article 157 (12) of the Constitution says that Parliament may enact legislation conferring powers of prosecution on authorities other than the Director of Public Prosecutions. It is quite different in tone and import from clause 9 which say that the powers of the DPP may be exercised in person or by subordinate officers acting in accordance with general or special instructions.
Article 157 (9) and section 22 (1) of the Office of the Director of Public Prosecutions Act, 2013 say almost the same thing, the difference being one of emphasis rather than constitutional and statutory intent. Section 22 (1) says that the DPP may, subject to such conditions as he or she may impose in writing, delegate any power and assign any duty conferred on him or her in terms of this Act or any other written law to a subordinate officer. Section 13 (1) describes the DPP's subordinates: Deputy Directors; Secretary of Prosecution Services; Prosecution Counsel; technical staff; and such other members of staff of the Office as may be appointed from time to time.
In my considered (and jaundiced view), the DPP's "subordinate officers" do not include the Commissioner-General of the Kenya Revenue Authority, the Commissioners responsible for administering the various taxes, of the other officers and staff of KRA. But I have been wrong in the past, so don't take this as cast-iron-solid legal advice.