I had a pair of Snell B Minors (which I just sold) that had non powered side firing 12's. I could never get the bass I needed no matter what I did. The big subs in mains are sometimes hard to locate in the room for the best response (especially in my case where I could not move them around). I really have no choice but to use a powered sub due to the fact I have to have narrow mains because of space limitations.
In several reviews I've read (from the more reputable reviewers IMO) on large mains with large powered subs included in the mains it appears that in many instances with good mains they state the mains can handle the low end without a separate powered sub, but they also stated that adding a separate powered sub, they could tell a difference. Of course that might be a matter of opinion.
I would strongly recommend the BFD(Behringer Feedback Destroyer) equalizer at a street price of $130 or so. It has 24 bands of equalization and is the most flexible eq I have found. I don't own one but will very soon. Do a search on reviews for this eq and you should find it is the eq of choice for many home theater systems. Keeping in mind that a "dip" in response "due to room acoustics" can usually not be tamed with an eq but rather only by moving the speaker to a different location ...sometimes only inches at a time. "Peaks" are easier to remove with the eq though. If you can position the sub or mains where you only had peaks then the eq would be a great tool. Unfortunately the BFD only comes in silver, but you could hide it possibly, that is if the rest of your system is black.
