No personal knowledge but there have been quite a few previous threads about Mulungu alone and with kava. If you search in the search bar you can find a lot of people have tried it. I think the general consensus is that both together are very sedating - maybe too sedating and some got decent headaches from combining. In general, I can't really recommend combining kava with other potential sedatives or psychoactive substances.
As often mentioned, the best way to drink kava is as medium grind, trad prep. But the best way to drink mulungu is as a high quality extract. The Tropical Link in Brazil makes a great product: safe, potent, legal, and ships via Fed Ex quickly to the states. Fabio provides full documentation of quality in each shipment.