low bass is the most power hungry
what model sub?
what amp(s)?
at issue is whether you send ALL frequencies to the amp and it then continues to makes low bass (ignore the speakers for a moment) or if you 'offload' low bass to the sub and then everything else above that to the amp, then to the speakers.
at issue is whether
1. the amp tries to make low bass or if a self-powered sub makes it's own low bass
2. all frequencies prior to sub crossover, jumpers in place: if the signal contains all frequencies, then the woofers will still be trying to make low bass
or, low bass removed by sub crossover, jumpers in place, the woofers only try to produce upper bass. the sub's adjustable crossover is of importance here.