An IT audit is an independent, point-in-time assessment of current state and risk; managed IT is a continuing operating model that runs your technology day to day. They are complementary, not alternatives.
The audit is independent by design and can be conducted without an MSP contract or NXDC relationship. Managed IT answers "who is going to keep it under control every day from here on".
A common sequence is to audit first to establish an evidence-based baseline, then decide which operating model matches the findings.