Some like the RELs can be run off the power output of the amp, one on each channel. I run mine this way. Two are better than one but if the choice is between one really good one and two so- so ones I would go the good one, you could always add another later. I have often turned one of mine off for some reason and not noticed that only one is running. I use mine for music and cross them over much lower than the typical HT set up. My HT also uses subs , there I use either an electronic crossover or a passive box run off the power outputs of my main amp to drive the sub amp. The RELs are of course powered subs.