I have a Knight long range hunter, which is built around the extreme breechplug. To answer your question, yes you can shoot BH 209 with this set up. I was shooting it with the original bare 209 primer plug, and that worked pretty well, but got the Lehigh conversion that uses a screw out / replacable vent liner to increase the flame reaching the powder.
It should work well for your rifle and BH 209.
http://lehighbullets.com/products.asp?cat=28If Knight is making one that works better, I am not aware of it.