Yeah, the first few maps of Siege of Bordrin's Watch were done on a chessex map with vis a vis and the artist felt limited. That's when we switched to the graph easel pad and prismacolor markers so she could go nuts.
I'll second both the amazingness and the Gaming Paper suggestion. We use Gaming Paper at our table and, although our results are substantially less artistic than yours, it works very well.These are amazing!
Have you looked into Gaming Paper? The easel is a good option, but Gaming Paper may work better for your guys. If not, rock on. But I really hope you guys keep those maps around.