You are headed in the right direction by starting with a REL. I have a REL, and this is the last sub woofer that I will ever buy. This sub blends in so well with my mains, that I don't know that it is there until I turn it off, and then I miss it. If your mains have plenty of low base, you probably can do without one, but in my opinion a sub fills out what is already there in a recording, that main speakers sometimes cannot reproduce. The key is to make it blend in so that its not just a boom box.
