No experience with the combination, but I would imagine almost any psychedelic would overpower Kava to the point that the effects of Kava would not be noticeable. Psychedelics are some of the most powerful drugs there are. Most are so powerful that they completely negate even the effects of large amounts of alcohol. I dont see how combining them would yield any worthwhile results, at least none that couldn't be experienced with the psychedelics alone. I would love to hear other opinions though. There may be some mild psychedelics that are not coming to mind.
Edit, marijuana(mj), being considered a mild psychedelic, can be beneficial to some at very low doses when combined with Kava. I believe they would amplify the effects of one another.