As I vaguely recall it, the SDA series used some sort of out of phase or similar signals from each speaker designed to cancel out some extraneous signal from the other speaker and thereby create a more holographic soundfield. I just didn't like it as much as their monitor series that they had at the time (and their Lsi-15 is a much better speaker than the old monitor series, in my opinion), which had a much cleaner sound and didn't sound tilted towards the bass to the point of muddiness down in that region like the SDA. It could be I heard a bad setup, but it was at a long-time Polk dealer that usually paid attention to set-up issues. However, I recall from some past threads that there are A-gon members who own and love the SDA speakers; you might want to search the archives to find them and ask for their thoughts on them (maybe in the Speakers to hold onto for life thread?). As I said, though, I felt the presentation was sufficiently different from the usual speaker system to require that you hear them before you pull the trigger on them.
