Working with ExtJS grid was kind of cool. But if you need to have another grid within the grid, the Grid selection, checkbox and expand column become hair wire on ExtJS.
I've tried several ways, but some how given up on it. Hope fully ExtJS 3.4 or higher could see the light on this feature...
After searching around, DHTMLXGrid did serve the purpose pretty well.
But the documentation is a bit confusing, need a bit of digging on the doc and the code in order to configure things up to what you might need.