A friend of mine has a large pair of SDAs. I'm not sure of the model, either the SDA Signatures or 1As. They have 8 6.5" drivers, 4 1.5" tweeters, and a 15" passive radiator. These speakers can move a serious amount of air without sounding strained in the least. They can sound boomy in the wrong environment however. My friend has them bi-amped with a ML 23.5 on the bottom and a ML 29 on top. He uses a GML parametric studio eq with the ML 23.5 to control the bass peaks in his room. With the GML engaged the Polks sound very clean at high volumes from top to bottom, with a wide and deep soundstage. Bass response is flat to 18hz. That said I do hear some cabinet colorations, and I don't think they're the most nuanced or tonally correct sounding speaker. His front end consists of a Placette RCV and a highly modified Kerns Sony 777ES.