I hate to say it, but you are S.O.L unless you want to go into the menu and turn the sub off when you use the b speaker, or you can negate the lfe and use high level connections to speakers a, or if you have an rs232 port on the yamaha you may be able to work around these setttings with a good PC based programmable remote. I do not work with yamaha gear, but the sub issue you are having is pretty universal among most entry/mid level consumer gear.