There are enough subs which have a complete crossover built in. Most of them are from pro brands and hence more expensive but there are also cheap ones like the JBL LSR310.A MiniDSP 2sx4HD is pretty cheap, especially if one already has an amplifier, does what an AVR does for Subs and is in roughly the same SINAD category. The hard part is most people don't realize they need an AVR or MiniDSP. I have LS50's, 2 Rythmik subs and a MiniDSP 2x4. The SQ is stunning, but it took me a few years to get it right. Most of that time was spent learning what to do.