I have the Sierra-1's with the RAAL upgrade, and have heard the Seos speakers on many occasions. My opinions are, (keep in mind this is highly subjective!), the Sierra's are better at low volumes, they have much better clarity, detail, and are super revealing. If your room is small, and you don't listen at reference level SPL's, they are extremely tough to beat. For music, they are unmatched. For movies, they are just a completely different flavor. Some will like them better than the Seos, and some vice versa. But, if your room is large, and you watch mostly movies at high SPL's, then the Sierra's will not give you the full wall of sound that the Tempest will. You really need to experience the RAAL tweeter to see for yourself whether or not I you want that type of speaker.