The point of AJAX is to reload only select sections of a page so site visitors don’t need to refresh the entire page. What you’ll essentially need to do is get the HT cart and the Aheadworks cart to reload together, because Aheadworks ATC extension doesn’t know there is a HelloTheme extension on the page. So to put it simply, you’ll have to modify the AW script to refresh both extensions, which I’d imagine is beyond the scope of theme support.
I’ve completely disabled my HT cart and took it off my site and just use the sidebar cart and top menu cart link, which update fine using the AW ATC extension. I’ll take a look at this in the coming few days, but I’m not a JS guy so I probably won’t be able to do much. Just a heads up.