The best product for powderpost beetles is Bora-Care. It is what the professionals use. Bora-Care will penetrate all the way through wood and kill anything in the wood that you treat and the best part is that it stays in the wood forever. However, the catch is that it can only be applied to raw wood, not wood that is painted, stained, or sealed. So, you have to sand off the finish and re-finish after applying Bora-Care, or you can drill holes where you see the issue and spot treat the infested areas, or inject into the wood after drilling holes in the areas.
Boracare is also the best product to use on raw furniture as it leaves the wood in its natural state.
Here is a link to Bora-Care if you would like to read further: http://www.domyownpestcontrol.com/boracare-p-100.html