Thinking I need a Sub...

I'm not in the Bob camp, in spite of how badly he wants me there. I'm merely speaking about the actual sounds of things, and if you adjust a REL to appear at the point where the main speaker starts to lose its ability to produce much bass and the REL takes it from there (below any main "crossover region" because that is irrelevant to the REL design), it works beautifully. There is no "muddying" of the main speaker's acoustic output because the main speaker is down some serious DBs at that point and (again, based on reality) blends fine if used properly. When you state things like, "The main speakers WILL MUDDY UP the clean bass produced by the REL, at least within the crossover region" you ignore the fact that there is no crossover region at the REL High Level input, simply a frequency point where you integrate the sub to assist the mains, and, clearly, you haven't heard a well set up REL or you would know this (maybe). I know other designs work well also, because I've heard them, and I'm IN the pro recording industry.

Completely agree with Wolf_Garcia, that's exactly how REL subs work and blend with the main speakers when setup properly.

Digital bass management compression/limiting nannys are not necessarily an advantage, they're simply designed as a "catch all" remedy for components that are badly matched to a room's acoustic properties. Of course things need to be "used properly," otherwise things are simply improper, if not tawdry.