My comparison probably isn't the best one, since I no longer have the SigDJs and didn't much care for them, but since you haven't gotten a response yet, here are my brief impressions: while they can both be impressive in their bass response, it seems to be in pretty distinctly different ways. The SigDJs definitely had significantly more impact-- in fact, I'd say they have the most impactful bass I've ever heard in headphones, period. (My experience is nowhere near as broad as some here, but nonetheless, the point stands for me). The SigDJ also puts significantly more emphasis on the bass than the LCD-2s, which present the bass in a much more linear (in relation to the rest of the spectrum) manner. Also, I'd say the bass on the LCD-2 is noticeably better textured and detailed, and while I wouldn't swear to it (this comparison comes from memory, not side-by-side like the others), I believe the LCD-2 went a bit lower as well. So in my mind, SigDJs dominate on impact, and the LCD-2 takes the cake on pretty much everything else.
Again, I may not be the best reference here, as I'm pretty deeply in love with my LCD-2 and didn't keep the SigDJs, but I think that others would probably agree with the broad strokes of my observations. Hope this helps!!
