almost everyone who has done the front sporcket change has had one hellavatime getting it off it seems! taking it on with poles and blocks of wood, haha...
i remember that there was a decent DYI on replacing the front sprocket, but i never get anywhere using the search option on this forum. someone else might remember the link, but i think you are doing what the other people have... using extension poles to increase leverage.
put a piece of wood through the back wheel and rest it on the swing arm, that prevents the sprocket from turning when you try and remove it.
from the manual:
makes it look a lot easier than it actually is i believe, lol!
good luck~