Basically, you can make holes instead of moving pieces each turn. If a piece goes to a hole, they get captured by the side that put the hole. You can put a hole at any place, excluding the locations of the current pieces.
Abandoned that letter system on my projects. There are also letters before the X's dictating the hole's colour. Also, white holes are dark grey, while black holes are... black. Also, if pieces move over a hole, like bishops or rooks, do they fall? What about knights, because they jump?