I've gone down this path before. If the mains are set to small there is indeed sound from my sub. If not there is not. But I normally have my mains set as small (like most people probably will), and would have to to futz in the menu each time to change it to large, and then back to small afterwards and so normally I don't bother to, and instead, just keep the mains small all the time because the double bass in stereo bypass to me just isn't a big enough deal to make it worth going through that hassle to eliminate it. YMMV.