I have never worked with Sencha Touch but I have worked with Sencha Ext JS.
You don't need an extension in order mix up Sencha ExtJS and Highcharts. All Highchart/HighStock charts are assigned an html div to which they are rendered. You only need to get the html div from the Ext Js element you want to use for your chart. Here is an example from code i have which works fine:
var myVp = Ext.create('Ext.container.Viewport', {.........}
chart1 = new Highcharts.StockChart({
chart: {
renderTo: myVp.down('#Graph1').getEl().dom,
zoomType: 'x'
},
............
............
});
Here is the Graph1, its somewhere in myVp
{
flex: 8,
xtype : "component", //i have other examples where the xtype is panel that
//work fine. I think this will work with all the type
//on containers
itemId: 'Graph1'
}
I know this isnt exactly what you were asking but i think its a very good aproach. The only drawback this has is that you will not be able to assigning a sencha store as the data of the chart. Here is the JsFiddle. Write me with feedbacks.