The great thing about a unit like the Behringer mentioned above: it is an inexpensive way to test the concept with your system. And even if you later want to focus in on just what features you want in a less electronic device, you can resell the Behringer.
Most folks I know either go with the SPL also mentioned above or with MiniDSP, which can give you Dirac at the same time.
Related to the Sublime... so you must pick frequencies in advance... here are kits for DIY: Collections – Xkitz Electronics
From the inventor of the RiPol subwoofer: Ridtahler: Produkte
I have a crossover to split surround sound left and right into midrange and tweeter built into a multiplexer from Ralph Stens. He also has both a kit, or he will build for you, a separate crossover: Active Crossover AFW1 - RStAudio.de
Like I said, recommend getting something easy to test with and to resell first, and then pick what you really want at what level of sophistication / electronics.