Such EQs are hooked to professional Power amps and they work well.....it does improve the sound quality and also boost output by 10 to 20% overall.....
In a home setup a lot of adjustments to be made along with home gear....your speakers need to ensure they are able to handle all those frequencies.....also the amp (power amp) should be able to handle EQ signals sent to it (10hz - 50khz ..min.) Else the sound will be muddle up etc...
A pre out amp (with main in) can be hooked to an EQ but this will be a pure stereo setup...... I am happy with Marantz as all their models have 9 Band EQ available for each speaker which can be manually adjusted.