I see from Worksaver's website that there is a 12" extension for the 30" augers. I wonder if the extension would fit the BX? I'd pose the question to the folks in Worksaver's sales: sales@worksaver.com
Actually, My 18" tree auger is working quite well on my BX2200, but I'm only digging down 18 inches with it. Of course, it eats shear pins like potato chips.. you need to keep a good supply on hand.