I have monoblocks and a REL Storm III sub and have never had the problem you described. The only thing I do differently is hooking up both the sub and satellite speakers to the same speaker outputs on the amp. I am not sure how your amp speaker outputs are configured--I would imagine them to be in parallel, which should allow you to hook the sub inputs to the other pair of speaker posts, but perhaps not. Perhaps you should try hooking them up with both the sub and speakers hooked up to the same posts and see if there is a difference.