I'm an insomniac and no form of kratom helps me sleep. Just throwing that out there. It actually keeps me awake, even the more "sedating" varieties. I thought that was pretty normal with anything hitting your opiate receptors though.
That combo will probably feel great but I don't know if it will help you sleep more than kava alone. Hopefully the pain relieving effects of the kratom last longer than the initial high, I don't have much experience treating pain with it.
I went to a kava and kratom bar on the east coast last month. They had kava and kratom tea, as well as a drink that had them combined. I didn't want to drop 13 bucks on it for various reasons, so I can't give you a report. I tried their kratom tea, I was curious how they could make something palatable with it (I always toss n wash). Turns out they use crushed leaf, not the micronized powder. Fun fact.