Presumably along with the 80Hz crossover for the surround (and center?) speakers, your fronts are set as "large" (full range). When you install the subwoofer, they all should be set to be small.
The quality of the speakers and the room's acoustics have the most effect on the quality of the sound you hear. Room EQ software (like MCACC) can help, but it's not a panacea (not to be confused with placebo
). The traditional rule of thumb is to spend twice as much on speakers as you spend on audio equipment. That really hasn't changed in many years, despite the temptations to ignore it when more sophisticated electronics becomes affordable to you.
Also, bear in mind that the manufacturer's speaker ratings are measured in an anechoic chamber. Their response in a real room is quite different, which is why running the EQ calibration is so important. Any changes in speakers or room layout require a recalibration, too.