Thought I would chime in on this discussion. I just bought a pair fo UCS1 subs and had a chance to breifly compare them to my LS1004s. Keep in mind that this was not a scientific sound experiment, just a down and dirty quick comparison.
I normally run a pair of LS1004 subs pushed by 2 RMX1850HD amps with EF500P tops. I hooked up one LS1004 to an 1850 and the pair of UCS1s to my other 1850. I didn't touch any of my processing (which is set up for the LS1004s). I played a variety of recorded music through both sets of tops and subs. I listened to each sub set one at a time. The pair of UCS1s definitely put out more sound than the one LS1004. The bass seemed to hit harder and was much cleaner sounding. The dual 18's seemed muddy and not well defined by comparison. I then unhooked one UCS1 and listened to a one-one-one comparison. The LS1004 put out just a bit more than the single UCS1, but not by much (to my ears).
Like I said, this was not a professional scientific experiment, just a quick review of both subs. With some processing tweaking, the UCS1 may even put out more sound. I don't know if a pair of USC1 will put out as much as a pair of LS1004 (didn'have a 3rd amp so I couldn't hook up both dual 18s), but I bet it would be close. I'm sure that 4 UCS1 would outperform 2 LS1004 by a wide margin. I will test this if I ever get another pair of UCS1s. Don't flame me for this information....this is just my observation from a 15 min. listening test.
I will be putting the UCS1s in a live music environment on Dec. 20th so I'll see how they do compared to the LS1004s.
Greg