Hi Dave,
Who the hell am I to tell you anything about audio?!?! Having said that, you might be interested in the crossover strategy used by Satterberg for their woofers for the LS3/5A. They used a 175 Hz 3rd order low pass for the woofers, and a 1st order at the same frequency for the high pass. My understanding is that they were trying to roll off the "BBC bump" built into the LS3/5As that gives them the illusion of bass when they're used separately. This site has lots of info about them:
https://sites.google.com/site/mpbarneys ... ergwoofersI had a pair of Chartwell LS3/5As in college, but sold them to my girlfriend when I jammed a pair of Magnepans into my dorm room. I lucked onto a pair of RAM LS3/5As (for $8!) a number of years ago, and then found a pair of the Satterbergs to complement them. (I remember reading the review from The Absolute Sound in the link above, and I had the brochure from HiFi Haven in New Brunswick, but never had the $$ to make the purchase at the time.) The RAM/Satterberg combination is tolerated in the living room, much more so than my unholy DIY open baffle abominations would be, so that's an advantage.
Sorry to be so wordy- and off topic, come to think of it. (Weren't we talking about summing?)
Anyway, I hope this is of some interest.
Stay healthy, folks!
Pete