SPL when designing

I am in the process of designing some speaker cabinets with Vituix Cad.  Got a question.  The main speakers will be driven by a flea watt 6 watt amp.  The sub by a Hypex 250 watt amp.  Should I try to match the efficiency of the drivers even though the subwoofer and mains will be driven by separate amps.  If I want the preamp to be the main volume control (I hate setting the sub all the time), would it help at all?