Is there any way to get volume control from the tv to affect the rca output?

Currently, I have two stereo speakers running off of a two channel amp from the rca out of the tv. I have just purchased a 15 inch powered sub. I read in the subwoofer forum that the sub out is affected by the tv volume control. Is this true for my tv? Is there any way to have the rca outs to also be controlled by the tv volume? Right now I have to change the volume in two places, it would be nice to have a single control.