I think a sub is a band aid in the scenario outlined. The right approach (happy path) is to fix the speaker/amp mating first and go from there.
Do subwoofers really help?
Easy question here all...if you mismatched your amp and speakers (meaning your amp has trouble with the load of the speaker), do Subwoofers really fix that problem? Is it smarter just to sell your speakers and get ones that better match the amp?