I promise not to use phrases like "better than", "not as good as" or "I wouldn't be caught dead playing this".
I finaly got my hands on an SD1 today, played with it for about an hour. First impression: it looks great and has a very pro quality look. The keyboard action(feel)is very nice. To my touch it is not the same as the X1(a little heavier). As with all the NEW KB's they are an extension of the previous model. The SD1 is very similar to the X1 both in sound and operation. The statement "If you like the X1 you will love the SD1" rings true! The Piano is very good across the whole keyboard! There is a better selection of sounds, in particular the Brass, Guitar and Woodwinds. The drums are very impressive. Nice brush sound, very realistic. The Electric Piano sounds are adequate not as impressive as the others. When selecting a style or Block Registration you can press 1 Touch(like the X1) but the difference is the sounds are displayed along both sides of the screen without covering any of the other info. On the fly you can select any one of the sounds in the 1 Touch memory(8 pages, 80 sounds,more user friendly than the X1)The Vocalist function is nice (a red LED indicates when it is on)and you can edit on the fly. Overall the layout is much better than the X1, although not as easy as the Yamaha, toss up between SD1 and the PA80.
Now for the sound!! It sounds very impressive but then again I liked the X1. What you have in the SD1 is a New and Improved X1, and there is nothing wrong with that!
How does it compare withe the PA80? To make it simple (1)the sounds, to my ears, are more substantial. What does that mean? Not better but fuller,warmer,realistic...etc. This is one man's oppinion!! What I translate as fuller..etc.? Someone else could find unappealing! (2)Styles? I will not compare styles, that is too subjective. (3) It really looks like a pro KB! The PA80 does not, once again one man's oppinion.
For me the SD1 is a better choice.
PLUSES: 3fills/Intros/Endings + break, To end(great feature)LowZ Mic input, Quality keyboard, more usable styles(for what I like to play). The one problem I experienced on the X1 has been resolved on the SD1. This was when you stored, in a Registration, Reverb and Delay levels for the Mic it would not hold, now it does(great feature). The PA80 is a good choice at its current price price. It will be even better if Korg keeps improving it(software/features). That's my two cents worth!!