Here are my considerations so far.
First of all, it would be nice if more users of well-placed DD-18 subs (or similar) in fairly large rooms would chime in with their actual listening experiences in this debate.
What I hear in a situation with a good system and room, is a detrimental effect due to engaging the crossover in the sub. In many other situations, this may instead be a big plus, overcoming the minuses.
In my situation, I am not so much using the sub for what it does to the bass, since I have full-range speakers anyway, but more for what it does to the overall musical impression. The DD-18 helps my main speakers to "throw" the music at me and establish a depth perspective. It is the first of many subs I've used that I really liked. I had a Sunfire sub that was amazing although it danced along the floor and distorted a lot, and then, a Bowers and Wilkins that could never be woken from the big sleep. I next changed to a pair of REL Strata 3 that were quite good, but one DD-18 was even better.
This discussion concerns sub setup for augmenting speakers in fairly large rooms. My impression is, that if the positional and analog setup is good enough, it is best to "defeat" the crossover and the associated electronics. However, there is some give and take at this point, my best electronic presets with the DD18 sound very good also.
