My add-on feet came in. Unfortunately, the Asgard 3's original feet are too big to fit in the holes on the tops of the add-on feet, but there is a kind of circular depression where the original feet can sit. It's fairly secure and unless you bump it very hard, I don't think the amp is going to move. There are rubber bases on the bottoms of the add-on feet.
Thanks to all who posted about add-on feet and spurred me into ordering some. I like the results. My Bifrost already feels much cooler to the touch.